English slang expression which can be used as a noun or a verb:
1 Knock off (noun), an item intended to look like something it is not, such as an expensive watch or designer clothes.
Knock off (verb) can have a number of meanings depending on context:
2 to stop working for a short break;
3 to leave work at the end of the day;
4 to steal or remove;
5 to kill or severely chastise someone;
6 to try to get close to someone for romance or casual sex;

One who has a mania for music.

An imitation of a major Brand Name

(n.) knockoff - a copy of an original brand, often priced dramatically lower than an authentic. Commonly, the designs will have been altered a bit, or they will appear the exact same, but some small detail may prove they are not authentic.

An item that looks exactly like an original product but lacks the expensive designer label and is replaced with a fake one. Usually costs half the price with half the style appeal.

a cheap imitation

Australian, to end the days work, to clock out.
2) colloq to steal