A jack of all trades is someone who has skill in many different areas. You might think of yourself as a jack of all trades if you can program computers, fix plumbing, and bake a mean cupcake.
Someone who's a jack of all trades is typically — though not necessarily — a man. While you can describe someone this way who is very good at many different types of jobs and projects, there's sometimes an implied ending to the phrase jack of all trades, which goes like this: and master of none. In other words, a person who dabbles in things but never gets really skilled at any one thing. Both versions of the phrase have been used since the 1600's.