Difference between _Bool and bool types in C?

These data types were added in C99. Since bool wasn't reserved prior to C99, they use the _Bool keyword (which was reserved).

bool is an alias for _Bool if you include stdbool.h. Basically, including the stdbool.h header is an indication that your code is OK with the identifier bool being 'reserved', i.e. that your code won't use it for its own purposes (similarly for the identifiers true and false).

There is no difference.