what is size_t in c

/*
The datatype size_t is unsigned integral type.
It represents the size of any object in bytes and is returned by the
sizeof operator.
It can never be negative.
*/

size_t is an unsigned integral data type which is defined in various header files such as:

<stddef.h>, <stdio.h>, <stdlib.h>, <string.h>, <time.h>, <wchar.h> 
It’s a type which is used to represent the size of objects in bytes and is therefore used as the return type by the sizeof operator. It is guaranteed to be big enough to contain the size of the biggest object the host system can handle. Basically the maximum permissible size is dependent on the compiler; if the compiler is 32 bit then it is simply a typedef(i.e., alias) for unsigned int but if the compiler is 64 bit then it would be a typedef for unsigned long long. The size_t data type is never negative.