It defines a pointer-to-function type. The functions return void, and the argument list is unspecified because the question is (currently, but possibly erroneously) tagged C; if it were tagged C++, then the function would take no arguments at all. To make it a function that takes no arguments (in C), you'd use:
typedef void (*MCB)(void);
This is one of the areas where there is a significant difference between C, which does not - yet - require all functions to be prototyped before being defined or used, and C++, which does.
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