This is the 5054th most frequent Russian word.
мешок
Bag; sack.
Here, 'мешок' is used in its primary sense as a 'sack' or 'bag', referring to a physical object for carrying things.
Он нес тяжёлый мешок на плечах.
He carried a heavy sack on his shoulders.
In this sentence, 'мешок' is used metaphorically to describe someone's appearance or behavior humorously or critically, implying they are slouchy or uncoordinated.
Ты напоминаешь мне мешок картошки!
You remind me of a sack of potatoes!
Here, 'мешок' is used figuratively to describe a curious or peculiar design or stain on a shirt that resembles a sack shape.