What does ‘Jack of all trades’ mean?

‘Jack of all trades, master of none’ is a figure of speech used with reference to a person who is competent with many skills but is not outstanding in any particular one. The phrase was in common use during the 1600s and was used as a term of praise. ‘Jack’ in those days was a generic term for ‘man’. Later, the ‘master of none’ was added and the expression ceased to be flattering.