Playing by ear is when a person can hear a song and without sheet music or even chords, they can play it. Not necessayly exactly like the song. But they can find out the tune usually on a piano or a guitar and play it.

A lot of people who are gifted with the talent of playing by ear were raised in very musicals homes. Whether this means being taken to a very musical church every Sunday or taken to concerts or the orchestra.

Although it is rare. There have been some people who had no musical influence what-so-ever from their family who can play very well by ear. Mostly because they have listened to a lot of music or just practiced a lot.