The meaning of the command label in Linux Manual

If you look at the Linux manual (for example, execute: Man Open), you will find that there are expressions in the document: Read (2), write (2), Lseek (2), Fcntl (2), and so on, what does the numeric expression in parentheses mean?

You can get the answer by command: Man 1 man: 1 user commands (such as LS, PS, etc.) 2 system calls (such as Open,read,write,lseek, etc.) 3 C library functions such as MEMCP Y etc) 4 devices and special files (such as/dev/under File) 5 file format and use constraints (such as/etc/passwd format) 6 Games 7 Reviews etc assorted things such as S Ignal Introduction) 8 System management tools (such as mount) in fact the number represents the area in which the document is located in manual, a total of 8 areas, such as the 8 area of all documents can be viewed: http://man7.org/linux/man-pages/man8/

The meaning of the command label in Linux Manual