Typedef

typedef is a keyword in the C and C++ programming languages. The purpose of typedef is to assign alternative names to existing types, most often those whose standard declaration is cumbersome, potentially confusing, or likely to vary from one implementation to another.

Under C convention (such as in the C standard library), types declared with typedef end with '_t' (e.g., size_t, time_t).

Read more about Typedef:  Using Typedef With Type Casts, Usage Concerns, Usage in C++, Other Languages