The term "chord" usually applies to three or more notes played together. However, in Rock and other modern styles of music, two notes played together are often called chords as well. This especially applies to the formations shown below which are called Power Chords, or fifth chords. The symbol for these chords consists of a letter name and the number 5 (E5, A5, D5, etc). The letter name (also known as the root note) refers to the first note of the chord. E.g. the root note of an A5 chord is A. The 5 refers to the other note which is a 5th interval above the root note. An interval is the distance between two notes. All you need to know is the root note of the chord and the fingering. Remember that only two strings are involved in a power chord. The dotted strings are not played.