This is the 12810th most frequent Russian word.
куб
Cube.
In this sentence, "куб" refers to the geometrical shape.
Он построил куб из деревянных блоков.
He built a cube out of wooden blocks.
Here, "куб" refers to a small, solid piece of ice in a cubic shape.
Куб льда медленно тает в стакане.
The ice cube is slowly melting in the glass.
"Куб" in this case represents the concept of a cube as a geometrical figure studied in mathematics.