[uhl]

More like tetris as in Tetromino: https://en.m.wikipedia.org/wiki/Tetromino

[zwp]

"Tetra" isn't completely unknown in English but perhaps the link is more obvious to Russian-speakers (the original author was Russian)? Is четыре/chetyre a cognate of Greek-derived tetra?

https://translate.google.com/?sl=en&tl=ru&text=four