When deaing with electrical boxes, what is the difference between "old" and "new" work?

Old work - existing house New Work - brand new home build

Old work is for older homes... usually every home that has every wall and ceiling closed up by drywall. New work is really for anything that is framed, but not closed up by drywall. Use old work to replace a light switch or outlet. Real easy to install with a drill.

Old work boxes are designed to be cut into existing wallboards requires wire to be fished inside wall. New work goes on exposed wall studs. Usually easier because everything is exposed.