C Language Learning--xxx_t data type uint8_t What kind of data type

What data type is uint8_t?

In the extended language of C, you will see a lot of data types that you don't know, such as uint8_t,in_addr_t. But these are not new data types.

What exactly does the _t mean.

It is a structural annotation that can be understood as a type/typedef abbreviation, indicating that it is defined by a TypeDef, not by other data types.
Uint8_t,uint16_t,uint32_t and so on, just use a typedef alias to type. typedef it will work well for the maintenance of your code. For example, there is no bool in C, some programmers use int, some programmers use short, it is more confusing, it is best to use a typedef to define, such as:
typedef char BOOL;

the *_t type for general shaping is :
1 bytes uint8_t
2 bytes uint16_t
4 bytes uint32_t
8 bytes uint64_t

header file Definition :

typedef signed Char int8_t;
typedef unsigned char uint8_t;

typedef int int16_t;
typedef unsigned int uint16_t;

typedef long int32_t;
typedef unsigned long uint32_t;

typedef long Long int64_t;
typedef unsigned long long uint64_t;

typedef int16_t intptr_t;
typedef uint16_t uintptr_t;