Wikipedia

Tankie is a pejorative label generally applied to authoritarian communists, especially those who support acts of repression by such regimes, their allies, or deny the occurrence of the events thereof. More specifically, the term has been applied to those who express support for one-party Marxist–Leninist socialist republics, whether contemporary or historical. It is commonly used by anti-authoritarian leftists, including anarchists, libertarian socialists, left communists, democratic socialists and reformists to criticise Leninism, although the term has seen increasing use by liberal and right‐wing factions as well.

The only time I've seen it be applied to anarchists is when Reddit libs don't like anyone left of them doing stuff like protesting, but normally the Wikipedia definition is how I see the word used.