Dominant
Fifth degree of a scale — creates the tension that resolves to the tonic.
The dominant is the fifth degree of a scale. In C major it is G; in A minor it is E. Its role is to create a tension that 'calls for' resolution on the tonic. The dominant → tonic progression (V → I) is the most fundamental cadence in Western music. On guitar, knowing how to identify the dominant of a key helps with improvising and stringing chords together intuitively.