A tankie is a Soviet communist apologist/Stalin fetishist. Communism by itself isn't something you need to really defend in that way, as it just means that the plan is to distribute the means of production and decision making abilities. For example Tito in Yugoslavia held a multiethnic state in the fucking Balkans so well to the point that people still identify as Yugoslavs even if its not an ethnicity but a state affiliation for a country that hasnt existed for 30 years. Same thing goes for Greece, WW2 would have been a complete Nazi victory if the communist partisan militias hadnt held up the Italians and Germans for so long.

The thing with tankies is that they are too blinded by ideology to notice that the Soviets and Maoists were/are just Totalitarians in disguise.