A more thorough explanation:

The United States Code Annotated (USCA) is a collection of books that contain the complete text of the United States Code, which is a compilation of federal laws. The USCA also includes historical notes, cross-references, and casenotes of federal and state decisions that interpret specific sections of the Code.

For example, if you were looking up a law in the USCA related to taxes, you would find the text of the law itself, as well as notes about how the law has been interpreted by courts in the past. This can be helpful in understanding how the law has been applied in different situations.

The USCA is an important resource for lawyers, judges, and anyone else who needs to understand federal laws and how they have been interpreted over time.