Why do programs in Unix-like environments have numbers after their name? [duplicate]

Answer 1

That's the man page section number. For example

 man printf

(should) Give you section 1, printf the bash command, while

 man 3 printf

gives you the C function printf.

Answer 2

It's the man page section. From memory, section 1 is user programs, 2 is system calls, and 3 is standard C library calls, and 5 is file formats.

Wikipedia has the full explanation here.