Well I am sure everyone must have come across many chrome or mozilla extensions like adblock, pocket etc… bus
but there is something called compiler extensions
compiler extensions are some features that are provided by specific compilers (like GCC) which are not a part standards of that particular language.
e.g:– typeof() is a compiler extension for C. it is used to find out the type of the variable. but this is not a standard ISO feature of C language, but just provided that compiler.