Parallel harmony consists of a single melody and one or more copies which are transposed by scale.
Parallel harmony is a melodic approach to harmony. It starts with an existing melody and then creates as many copies of that melody as are needed. The aim of parallel harmony is to reinforce the original melody by repeating it.
In two part parallel harmony there is one melody and one copy. The copy of the original melody is the parallel melody. It is transposed up or down by a chosen interval. The original melody and the parallel melody together create two part parallel harmony.
There is only one melody in parallel harmony and only one decision to make: which interval to transpose by. We start by looking at the four options: parallel octave, parallel second, parallel third or parallel fifth. A power chord contains a parallel fifth and a parallel octave and, as it is often associated with the guitar, we have a look at tablature, which is another way to notate music. We end with writing multipart parallel harmony.
Parallel harmony is quick and easy to write. It is simple enough to enable you to quickly construct an interesting harmony to sing or play.