It means the time that you finish work, and are free for the rest of the day. When do you get off work? What time do you get off? Are you off tomorrow?

Just yesterday, my coworkers and I were all saying "Oh my gosh, I can't wait to get off work!" because we were all anxious for our work day to be finished.

"To get off from work" simply means to leave work as in one's office. When making plans with friends or such you can say "I get off from work at XX:XX time" to let them know when you will be available. Of course this can differ based on context, if you would like a more precise explanation please feel free to provide some example sentences.