A jack of all trades is someone who is capable of performing a variety of different types of work, although he or she may not be particularly skilled in any particular field. The term emerged in the 1600s as part of a larger phrase, “jack of all trades, master of none, though oftimes better than a master of one.” Depending on the usage, the term can be complementary or somewhat negative. The term is also sometimes used, albeit rather incorrectly, to describe a Renaissance man.
If you're curious to know more about the word origins behind the phrase, the use of the term “jack” to describe a common man dates from the mid 1300s. The name “Jack” has historically been very common, and it is also the root behind words associated with masculinity, like male animals and some tools.
There are a number of ways to think about a jack of all trades. People who think of the term as negative usually suggest that it implies that someone knows a little bit about a lot of things, but not enough to accomplish anything meaningful. On the other hand, one could also think of this person as an individual with many talents and skills; a contractor, for example, may bill him or herself as a jack of all trades, suggesting that he or she is capable of performing a wide range of tasks for clients.
Hiring a jack of all trades can be a sound decision for someone who needs several small tasks accomplished around the house. Rather than hiring a plumber, a construction worker, and a bricklayer, for example, a homeowner could hire one person to accomplish all three tasks. This is often more cost efficient, especially with small jobs that do not require a high level of skill. In this sense, this person might also be called an “odd job man.”
The meaning of a “jack of all trades” is slightly different than that of a “Renaissance man.” A Renaissance man or polymath is someone who is skilled in a variety of intellectual, rather than physical, pursuits. He may certainly also be talented physically, but the term is more commonly linked with people like Leonardo Da Vinci, who had a number of intellectual talents ranging from a keen scientific mind to an outstanding artistic ability.