Chords are the basic notes that make up a harmonious sound. They can often be heard together or directly after each other in some sort of a rhythmic arrangement. They are usually made up of a root note, which also tells you the key signature the song is in. Chords can then have a closing note, which is the last note of the chord. Everything that is played in between is what makes the chord what it is and uniquely set aside from any other chord.