Possible Duplicate:What do the numbers in a man page mean? All system calls described in manpages have an associated number such as exec(3). What is the meaning of this number?
What means the integer argument in system call descriptions?
man;system calls
The number is the man section. The 3 is for library calls. Here is the full list from man(1):   1   Executable programs or shell commands   2   System calls (functions provided by the kernel)   3   Library calls (functions within program libraries)   4   Special files (usually found in /dev)   5   File formats and conventions eg /etc/passwd   6   Games   7   Miscellaneous  (including  macro  packages and conven       tions), e.g. man(7), groff(7)   8   System administration commands (usually only for root)   9   Kernel routines [Non standard]Some things have the same name in different sections. For example, man(1) is for the man binary, while man(7) explains how the macros should be written for manpage formatting. To access a specific section, you can put the numerical argument before the item:man 7 man