When you do man cat, you get an output like:
CAT(1) BSD General Commands Manual CAT(1)
NAME
cat -- concatenate and print files
Ever wonder what the 1 in CAT(1) stands for? It’s the section for command as defined in Unix Programmer’s manual. Here’re the sections:
1. Commands
2. System calls
3. Subroutines
4. Special files
5. File formats and conventions
6. Games
7. Macro packages and language conventions
8. Maintenance