QUOTE(hello_cello @ Sep 2 2009, 04:47 PM)

Ternary form is usually said to be ABA, but in reality, it can be anything made up of one section sandwhiched by another two sections, which are practically the same, such as AABBAA, AABA etc.
The AABA form is very common in many 19th-century operatic arias. In this context, the form is also known as the "quatrain form."