驴友 is formed by combining the character 驴, meaning "donkey", with 友, meaning "friend", where 驴 is used phonetically to substitute for 旅, meaning "travel", as in the word 旅游. This substitution creates a pun where 驴友 sounds similar to "travel friend" but literally reads as "donkey friend", resulting in an informal term for travel enthusiasts or backpackers.