It's usually time. I knew a guy that "worked" at Walmart. His job was collecting the carts. He would clock in, then go on about his day. When it was time to clock out, he would drive back and clock out.

It took 8 months for the store to realize this and fire his butt. In his case, it was a meeting. It was an All Hands, his timecard showed he was clocked in, but never appeared at the meeting.