imaginary

From cppreference.com
Defined in header <complex.h>
#define imaginary _Imaginary
(since C99)

This macro expands to a type specifier used to identify imaginary complex types. The macro is defined only if the implementation supports imaginary types.

A program may undefine and perhaps then redefine the imaginary macro.

[edit] See also

(C99)
complex type macro
(macro constant)