An olive was a type of fruit. It was used to create olive oil.

When visiting Simon and Joanne's apartment, the Fifth Doctor, Tegan and Turlough were offered gin and tonic, peanuts, olives and cheesy sticks. (PROSE: Lant Land)

At a 9th century feast, the Sixth Doctor ate fish, wine, bread and olives. (PROSE: The Man Who Wouldn't Give Up)

David Underwood claimed to be afraid of olives. (AUDIO: Through the Ruins)

When the Tenth Doctor warned everyone at Richard Lazarus's party to leave, a guest joked that the most dangerous thing there was choking on an olive. Ironically, she was subsequently attacked and drained by the mutated Lazarus, leaving nothing but her withered husk behind. (TV: The Lazarus Experiment)

The Thirteenth Doctor doesn't like olives and she notes that in order to explain why, she'd be there for weeks. (PROSE: The Good Doctor)