Pieces of music can usually be divided up into a few large sections that share common material. By seperating these sections of music we define the form, or structure, of the work. Take the beginning of this Musette by Bach:

 Bach Musette A section.aiff

Looking at the motivic structure and listening to the excerpt makes it clear that this is a question and answer phrase that stands on it's own. We will call this material the "A" section. Now lets add some completely different material, which we will call the "B" section:

 Bach Musette Binary.aiff

Now we have a piece in one of the most common forms in music, the AB form, also called binary form. Notice that we have added repeats. Sections of a piece sometimes contain one phrase, but they often contain multiple phrases that share common material and sound similar; in this case, our phrase structure is AABB. When analyzing form, we look for areas that contain clearly differnt material to define a section, so we call this a binary, or AB, form.

Now lets add a D.C. al Fine at the end of the B section, and an Fine at the end of the A section. A performer would play through the entire piece (with repeats), and then would go back and play the A section again. This gives us another of the most common forms in music, the ABA, or Ternary, form:

 Bach Musette Ternary.aiff

Verse/Chorus form is the structure most used in popular music. Similar to binary and ternary form, a song alternates between the verse and chorus a number of times. Often, it ends with an instrumental break or solo, followed by a repeat of the chorus. One simple example of a song written in verse/chorus form is Yellow Submarine by the Beatles:

Notice the sparse layout of this arrangement: only the melody, lyrics, and chord changes are given. This kind of arrangement is called a lead sheet. It gives only the essential information, and leaves the instrumentation and accompaniment style up to the performer.