It's original definition doesn't include liberals. I consider myself relatively left. I've had people ridicule some of my viewpoints for being too liberal (I guess too center for them). Those people were tankies, but they weren't tankies because they're more left than me. It's because they consider themselves to be very left leaning while still praising authoritative regimes and being apologists for them. That's the tank part. They're alright with military dictatorships of the past and even consider them to have been successful. They also rarely are able to admit the flaws of those regimes (including the genocides), and even if they do, there's a "reason" for it (X might have been bad and did this, but at the same time, it also did Y which was somewhat good)