trenje

1. (in physics, engineering) friction
   Ulje smanjuje trenje između delova motora. — Oil reduces friction between engine parts.
   Zbog trenja se guma brzo zagreva. — The tire heats up quickly because of friction.
2. rubbing
   Trenje ruku pomaže kada je hladno. — Rubbing your hands helps when it's cold.

For friction between people, Serbian usually says trvenje rather than trenje.