(Def 1)
A string that can be typed repeatedly in Gunbound to piss certain people off.
(Def 2)
Format code tag that literally means 'Replace this with a [niger]'. Orinigally introduced in the C programming language as a format specifier for the printf function, it was later adopted by a plethora of other languages such as java, ruby, etc.
(Def 3)
Escape sequence for the newline character in C and other programming languages (C++, Haskell, Java, Perl, Python...).