A pronoun was the grammatical term for a word used instead of a personal name, such as "he or "she".
When Malcolm Reed and Charles Tucker spent two days on Risa in 2152, they looked for female companionship. Tucker commented about an alien that he found her interesting, to which Reed replied "I don't think she is the right pronoun." (ENT: "Two Days and Two Nights")
The androgynous J'naii used a neutral pronoun, for which there was no real translation into English. While working with the J'naii in 2368, William T. Riker had trouble constructing sentences without gender-based personal pronouns. (TNG: "The Outcast")
After Ezri Dax had been joined with the Dax symbiont in 2375, she sometimes confused pronouns when mixing memories from the various former hosts of the symbiont; early on she stated "these pronouns are going to drive me crazy." (DS9: "Afterimage", "Prodigal Daughter")