trailer

any vehicle intended to be coupled to a motor vehicle excluding semi-trailers, and constructed and equipped for the carriage of goods

Also defined in

Regulation (EU) 2018/858 of the European Parliament and of the Council of 30 May 2018 on the approval and market… 32018R0858, Article 3, point (17)
any non-self-propelled vehicle on wheels designed and constructed to be towed by a motor vehicle, that can articulate at least around a horizontal axis perpendicular to the longitudinal median plane and around a vertical axis parallel to the longitudinal median plane of the towing motor vehicle;
Regulation (EU) No 167/2013 of the European Parliament and of the Council of 5 February 2013 on the approval and market… 32013R0167, Article 3, point (9)
any agricultural or forestry vehicle intended mainly to be towed by a tractor and intended mainly to carry loads or to process materials and where the ratio of the technically permissible maximum laden mass to the unladen mass of that vehicle is equal to or greater than 3,0
Regulation (EC) No 561/2006 of the European Parliament and of the Council of 15 March 2006 on the harmonisation of… 32006R0561, Article 4, point (b)
any vehicle designed to be coupled to a motor vehicle or tractor