Palm Muting – A guitar technique where the sound of the guitar is muted by resting the back of the picking hand across the strings while playing

(Pronounced parm myoo-ting)

To remember what palm muting is, it's essentially in the name: 

Rest the side of your palm on the strings you are picking to create a muted sound

The hand that is resting on the strings is always the one closest to the bridge of the guitar, while fretting hand's technique continues as normal.

Palm muting dampens the strings, shortening the length of time that the notes ring out for. Placing your hand further away from the bridge increases the muting effect.

The purpose of the palm muting technique is to create a tighter, more percussive sound or a rhythmic effect.