what is delay() in C? is it a system function? : in a book, I saw a piece of code.

[![command line aurguments][1]][1]

but when I ran this code it says
C:\Users\dipankar\Desktop\cla.cpp	[Error] 'delay' was not declared in this scope

they used it without proper documentation. they only said that "delay() is used to delay the execution of the next line by few milliseconds"!!.
please help.


  [1]: https://i.stack.imgur.com/WSOUm.png