what does imu mean code example

Example 1: what does $foo mean

It's just a placeholder

Example 2: what does intrinsic function mean

In computer software, in compiler theory, an intrinsic function (or builtin function) is a function (subroutine) available for use in a given programming language whose implementation is handled specially by the compiler. Typically, it may substitute a sequence of automatically generated instructions for the original function call, similar to an inline function.[1] Unlike an inline function, the compiler has an intimate knowledge of an intrinsic function and can thus better integrate and optimize it for a given situation.