What does the number mean in 'ls(1)', 'stat(3)' and 'apt(8)'? While browsing through the web and local documents, I often see expressions like this: See apt(8) for more information about the available commands. My question is, what does the number here stand for?

From the "man man":

MANUAL SECTIONS The standard sections of the manual include:


1 User Commands
2 System Calls
3 C Library Functions
4 Devices and Special Files
5 File Formats and Conventions
6 Games et. al.
7 Miscellanea
8 System Administration tools and Daemons

Distributions customize the manual section to their specifics,
which often include additional sections.