Differences among TOC, Cross-reference, and Index

TOC
A table of contents lists all the main chapters, titles, and the page number they start on. It may also list multi-level sub-chapters and descriptions in detail.
A TOC is always contained in Front matter of a book.
A TOC is used to search a particular chapter or sub-chapter in a book.
A TOC is always a sequential list.

Cross-reference
A cross-reference is a reference within the text to some other part, preferably on the body or book block.
A Cross-reference is mainly contained in Body.