To stop doing something, especially a job or activity. After years of working in the city, she decided to pack in her job and move to the countryside.
To fit a large number of things or people into a space. They managed to pack in over a hundred people into the small hall for the concert.
To cease or give up an activity, often due to failure or lack of interest. He packed in his attempts to learn the guitar after realizing it wasn't for him.