What is the meaning of when someone say play it by ear? Thank You?

Literally, you either play music by following a written musical score, or intuitively by hearing what you are producing but with no written scheme to follow.

The expression is also use as an analogy of this kind of approach to any other field, and has come to mean to decide how to deal with a situation as it develops rather than planning how you are going to react.

Not following a piece of music written down..playing it by listening to the notes and reproducing them by their sound.

Like winging it. So you make it up as you get new information, or as things pan out

to do something without special preparation <I don't know how they'll react to our proposal, so we'll just have to play it by ear and hope for the best.>

http://www.merriam-webster.com/dictionary/play%20it%20by%20ear

https://en.wiktionary.org/wiki/play_by_ear

Improvise

some people are musically gifted. with no training they are able to listen to a piece of music and then play (by piano, guitar, etc) this gift is known as being able to "play it by ear"

Play a song without sheet music, or more generally to do something without planning in advance.

play according to what you hear or heard?

go with the follow, be flexible

Improvise