To quote wikipedia

Tankie is a pejorative label for communists, particularly Stalinists, who support the authoritarian tendencies of Marxism–Leninism or, more generally, authoritarian states associated with Marxism–Leninism in history. The term was originally used by dissident Marxist–Leninists to describe members of the Communist Party of Great Britain (CPGB) who followed the party line of the Communist Party of the Soviet Union (CPSU). Specifically, it was used to distinguish party members who spoke out in defense of the Soviet use of tanks to crush the Hungarian Revolution of 1956 and the 1968 Prague Spring uprising, or who more broadly adhered to pro-Soviet positions.