Here's some definitions to better understanding trailing

AWD
Acronym: All Wheel Drive Typical in mini-vans and smaller SUVs. Different from the old conventional "4-wheel drive" in the fact it's mostly automatic and "computer" controlled.
Ball
The trailer ball is what attaches the trailer to the hitch. Ball sizes vary as do capacities by manufacturer. Balls also come in many different finishes.

Common Sizes:
Ball Height
Measurement from the ground to the top of the ball or ball coupling (trailer) when parked on a flat surface and parallel to the ground. Used to determine the amount of drop or rise needed in the ballmount to make the trailer ride parallel to the ground when being towed.

Ballmount (Ball Mount)
The part of a trailer hitch that slides into a receiver and fastens with a pin and clip to allow the attachment of a ball for towing a trailer.
Bumper
The part on a vehicle which protects the front and rear ends in the event of an accident, although some on trucks may have facilities for towing, the bumper should not be used as a towing device.
BUMPER TYPES
STEP A bumper which is intended to be used as a step.
STOCK The original bumper on a vehicle, (also refers to NOT a step bumper).
COWBOY Same as "deep drop".
Deep Drop A step bumper shaped like a "V" to lower the step surface in the center.
ROLL PAN Not really a bumper but a facsia panel used instead of a bumper. This bumper is common on lowered trucks.
OEM (Original Equipment Manufacturer) This is the bumper that comes on your vehicle from the factory. This term is used when only one choice is available from the factory.

Bumper-Pull Trailer
See Tag-a-Long
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-C-

Chassis
The frame of a vehicle. This is the main structure of a vehicle, which all other parts attach to regardless whether it is unibody or frame construction.
Class 1
Trailer Hitch with capacity of up to 2000# gross trailer weight and 200# tongue weight.
Class 2
Trailer hitch with capacity of up to 3500# gross weight and 350# tongue weight.
Class 3
Trailer hitch with capacity of up to 5000# gross and 500# tongue weight. Also sometimes refers to a hitch with a 2" receiver regardless of rating.
Class 4
Trailer hitch with capacity of up to 10000# gross trailer weight and 1000-1400# tongue weight. Although many times any hitch with a capacity greater than 5000# gross weight is referred to as a Class 4.
Class 5
Any Trailer hitch with capacity greater than 10000# gross trailer weight and 1000-1200# tongue weight. Usually a 2.5" receiver or in some special cases a 2" receiver.
Clip
Used to retain pin in receiver style hitch
Converter
Wiring converter: 5 wire systems to 4 wire systems. Used to integrate the stop circuit with the right and left circuits, with a diode on each circuit to prevent loopback to the turn signal switch...etc.
Coupler
The part of a trailer which attaches it to tow vehicle by going over and locking to the ball
Custom Hitch
One that is designed to fit a specific vehicle

-D-

Drawbar
See Ballmount
Drop-Down
A ballmount with a drop in it to lower ball-height, to make the trailer ride parallel to the ground.

-E-
Equalizer (colloquialism)
See Weight Distributing Hitch
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-F-
Fifth Wheel
A type of hitch that mounts in the bed of pickup truck; designed to be like hook-ups on big tractor/trailer rigs. It uses a plate in the bed of the truck, and a pin on the trailer.
Frame
The part of a vehicle which all other parts attach to. Frame usually refers to a non-unibody chassis.
French Link
A chain link with a space, allowing chain to be attached to it. The space can be closed with an attached threaded collar, thereby making the link once again integral.
FWD (acronym)
Front Wheel Drive

-G-

GCVW
Gross Combined Vehicle Weight: GVW plus the weight of any towed vehicles or trailers
Gooseneck
A type of trailer hitch which mounts in the bed of a pickup truck. Goosenecks use a ball in the bed (either 2-5/16" or 3" in diameter), and a coupler on the trailer, not to be confused with a Fifth Wheel.
Grey Market Car
Grey market cars usually have a label inside of the driver side door jamb that states that the vehicle was imported to this country and then retrofitted with approved impact absorbing bumpers and smog equipment to comply with U.S. rules.
GVW
Gross Vehicle Weight: The total capacity of a vehicle including all of its contents and passengers, and the weight of the vehicle itself.

-H-

Hitch Bar
See Drawbar
Hitch Weight
See Tongue Weight
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-I-

Insert
Any item which slides into a receiver hitch (i.e. Ballmount, Bike rack, Winch...etc.)
ITOR (Acronym)
Inside Top Of Receiver: A measurement from the ground to the upper inside edge of the receiver tube, used to help determine measurement for drop down or rise.

-J-

Jack Knife
Any time the trailer tongue collides with the tow vehicle from turning too sharply. Usually occurs while backing up.
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-L-

LB
Long Bed (i.e. Long Bed pickup truck or van)
Locking Pin
A hitch-pin which locks with a key to prevent theft of the ballmount or other insert.
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-P-

Pin
Used to fasten any insert into a receiver hitch. Available in standard and locking configurations
Pintle
A type of hitch that uses a round ring called a lunette on the trailer end. Sometimes referred to as a "GI" or military type hitch. Pintles have closing jaws, locking the lunette in . These are also available in pintle/ball combinations.
Pintle Mount
An insert for a receiver, having a shank with a flat plate to bolt a pintle to. These are typically adjustable for vertical height.
Plug
The connector used to connect trailer wiring to the tow vehicle; plug refers to the trailer end of the connection, Socket refers to the car end.
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-Q-
Quick Link
See French Link
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-R-
Receiver
The part of a trailer hitch that attaches to the frame of a tow vehicle, and has a receptacle for inserting an attachment
RWD
Rear Wheel Drive
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-S-

SB
Short Bed (i.e. Short bed pickup or van)
Shank
Socket
Wiring connector used on the CAR end of a trailer wiring connection. The plug is the end used on the trailer.
Spring Bar
The part of a weight distributing hitch which does the lifting. A "lever" bar typically is made of spring steel.
Sub-Frame
The part of the vehicle which supports the engine and front suspension on a unibody vehicle.
SUV
Sport Utility Vehicle
Sway Bar
A specialized spring which is part of the suspension on a vehicle. NOT part of a trailer hitch. Sometimes confused with a weight distributing hitch.
Sway Control Device
A device which goes between a weight distributing ballmount and a trailer to reduce the likelyhood of sway caused by passing vehicles and wind. This device should not be used to correct sway caused by improper tongue weight (too little or too much.)
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-T-

Tag-A-Long Trailer
A trailer that is pulled behind a vehicle with a chassis mounted trailer hitch as opposed to a Fifth-Wheel or Gooseneck.
Tandem axle
Two axles (four wheels)
Tongue
See Coupler
Tongue Weight
The amount of weight the trailer puts on the tongue of a trailer or on the ball of the hitch. This load is a vertical load. It should be at least 10% of the gross trailer weight.
Tow Bar
A device which attaches to the front of a vehicle which allows it to be towed by another vehicle.
Tri-axle
3 axles (6 wheels)
Trunnion
The replaceable end of a square bar weight distributing hitch which attaches to the ballmount.
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-U-

Uni-Body
A vehicle that has frame and body integral. Usually has a sub-frame for the front end which mounts the engine and suspension.
Universal Hitch
(NO SUCH THING) Some would have you believe that these exist. And they do, but the inherent compromises involved in making a hitch that fits "everything" makes them fit nothing correctly.
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-V-

V-5
A system of rating trailer hitches established by the Trailer Hitch Manufacturers Association (r){THMA}
VIN
Vehicle Identification Number
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-W-

WB
Wheel Base
Weight Carrying
A towing situation whereby all of the tongue weight is carried directly on the rear of the tow vehicle and on the hitch.
Weight Distributing
A towing situation whereby some or all of the tongue weight is redistributed by use of a weight distributing attachment through the vehicles chassis from the rear axle to the front.
Weight Distributing Hitch
An attachment, which slides into a receiver hitch, and redistributes hitch (tongue) weight. Typically uses 2 spring bars, one on each side of the trailer to lift up and apply leverage to the tow vehicle, thereby redistributing tongue weight from the rear axle to the front. This provides more vehicle stability while towing. Weight distributing hitches currently come in two configurations: One with square bars that hook to the center of the ballmount, called trunnion bars, and one with round bars that slide into the bottom of the ballmount, called round bars.
Weldnuts
Weldnuts is a term for threaded nut inserts that are already in the chassis installed by the vehicle manufacturer
Wiring System
3wire: Tail Lights, Left Turn and Stop, Right Turn and Stop(3 circuits): Usually used where the trailer ball provides a ground, which is not a good idea; the lights will flicker and shut down randomly.
4wire: Tail Lights, Left Turn and Stop, Right Turn and Stop, Ground (4 circuits)
5Wire: Tail Lights, Left Turn, Right Turn, Stop, Ground (5 circuits)
Most trailers are 4wire systems. When your vehicle is a 5wire and trailer a 4wire, a converter is required.
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-Z-

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