I have never before heard the term tankies used and before today would not know it meant a hard line communist.

@HubertManne The term "tankie" was originally coined to refer to pro-USSR communists who supported sending in the tanks to destroy Hungary and Prague's counter-revolutions in the 50's and 60's:

The term "tankie" 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.
The term is also used to describe people who endorse, defend, or deny the crimes committed by communist leaders such as Vladimir Lenin, Joseph Stalin, Mao Zedong, Pol Pot, and Kim il-Sung. In modern times, the term is used across the political spectrum to describe those who have a bias in favor of authoritarian states with a leftist legacy, such as the People's Republic of China, the Syrian Arab Republic, and the Democratic People's Republic of Korea. Additionally, tankies have a tendency to support non-socialist states if they are opposed to the United States and the Western world in general, regardless of ideology. source

The person above is correct that is has been a thing since the 1950s, but for most of that time it was a relatively rare term used to refer to the UK's communist party (which hasn't even existed since 1991) and occasionally for hardline old-fashioned leftists in general, again mostly in the UK. It's only in the past couple of years that it got picked up by the internet and went everywhere, which is probably why you haven't heard of it. I'm from the UK myself and I haven't heard of it until recently.