2.5. Chapters
Following are excerpts from the Unofficial DVD specifications Guide 2.2 ebook.

A sequence of one or more programs (within a Program Chain or PGC, PGC is covered on next page) with consecutive program numbers can be defined as a Part-Of-Title or PTT. PTTs are commonly interpreted as chapters, and are represented as units of random access provided to the user. Many authoring packages automatically assign one PTT for each program. In this case, each chapter corresponds to a program defined in the DVD project. The reason chapter is commonly referred to as Part-Of-Title will become obvious in the explanations of titles in subsequent section of this guide.


2.6. Graphical display of chapters
If a program is defined as a chapter, the chapter number is displayed as a label on the left side of the program icon.

The typical relationship of chapters and programs is illustrated in the Unofficial DVD specifications Guide 2.2 ...