The action on a guitar refers to how close the strings are to the guitar neck and frets. The closer the strings are to the surface of the neck (low action) the easier it is to press down the strings to play notes and chords. High action, where the strings are a further away from the neck and frets are harder to press down but notes will ring for longer and louder.
The trade off for low action is that the closer to the neck the strings are the more likely the strings will buzz. The buzz is caused by the string vibration, when the string is really close to the frets and it is vibrating because it has been strum the vibrations of the strings hit other frets. Not normally a nice sound. High action, where the strings are a further away from the neck and frets are normally buzz free but are harder to press down.
You’re more likely to see jazz players with a higher action and more metal guitarists with a low action. There are many exceptions though.