A term used when someone is sharing gossip about someone or something.

The tea about Prince Harry and Meghan Markle was piping hot.
History and usage

Tea is believed to have originated from Black drag culture. It can be potentially connected back to popular performer, Lady Chablis, who can be quoted in the 1994 bestseller Midnight in the Garden of Good and Evil: “Yeah, my T. My thing, my business, what’s goin’ on in my life.” T, here, is short for truth.

The word tea might be a riff off of Lady Chablis' T and tea parties, which many well-to do women are imagined to be gossiping over tea.

It's currently used in phrases like "spilling the tea", "give me the tea, sis" which is popular in Black gay slang.