A suspended chord is a chord that creates a subtle harmonic tension by adding an extra note that sounds like it wants to resolve back to the original chord. You can hear their use in most types of music. Technically the extra note is the 4th step in the major scale replacing the 3rd. Common symbols that signify a suspended chord are “sus” and “sus4”. They’re easy to learn, because you already know the fingerings for the original chord (just take the “sus” off and you have the original chord).
Play the E chord below and then add your 4th finger to the second fret
of the 3rd string. Do you hear how it sounds like it wants to resolve
back to the regular E chord? As a general rule you should always please
the ear by resolving the suspended chord back to the original chord.