dres

1. jersey; kit
   Kupio sam sinu dres Crvene zvezde. — I bought my son a Red Star jersey.
   Igrači su izašli na teren u novim dresovima. — The players came onto the pitch in their new kits.
2. (in u dresu) playing for a team
   U dresu reprezentacije postigao je deset golova. — He scored ten goals playing for the national team.

A tracksuit is usually trenerka in Serbia; dres is mainly a team kit.