Trailer Type.  Well that’s easy, we’re building a Box Trailer

Trailer Category.  Under 750kg, Very Light Trailer (TA).  That’s us!

Aggregate Trailer Mass (ATM).  The total mass of the trailer including the maximum load as defined by the manufacturer (aka me!).  Includes the mass imposed on the towing vehicle.  (AKA you can’t subtract the 30kg or whatever that it puts on the towball..)

Gross Trailer Mass (GTM).  The mass imposed on the ground by the tyres of the trailer.  So that’d be the ATM less the ball weight?  Hehe, ball weight, lol.

Tare Mass. The total mass of the trailer when not carrying any load, but when ready for service with all standard equipment and options fitted.  So including things like tent pole holders, or antenna mast mountings, etc.  Includes the ball weight.  So essentially GTM but unloaded..

Length. That’s towbar to rear of trailer.

Width.  Point from the side extremities, including lamps etc.