Ternary – The structure of a piece of music which is divided into three sections
To remember what ternary means use the following mnemonic:
Turn a really (ternary) complex song into a simple one by using a structure of three sections.
Binary form of music describes the structure of a piece of music which is divided into 2 different sections A and B where A and B are a contrast of sound often created by a key change.
A ternary form of music has 3 sections similar to binary except the first and third parts are essentially identical.
Ternary is therefore known as A B A music.