In C programming language, a token is the smallest unit of a program, which the compiler recognises. A token can be a keyword, identifier, operator, punctuation symbol, or a literal.

Keywords are pre-defined words in C that have a specific meaning and cannot be used as variable names. Examples of keywords in C include "int", "float", "if", and "for".

Conversely, identifiers are user-defined names given to variables, functions, or other entities in the program. Identifiers can consist of letters, digits, and underscores but must begin with a letter or underscore. Examples of identifiers in C include "count", "sum", and "result".

Operators are symbols that perform operations on variables and values. Examples of operators in C include "+", "-", "*", "/", and "%".

Punctuation symbols include braces, parentheses, semicolons, and commas, which are used to define the structure and syntax of the program.

Literals are values that are directly specified in the program, such as integer literals, floating-point literals, and string literals. An integer literal is a sequence of digits, such as 123, while a floating-point literal includes a decimal point, such as 3.14. A string literal is a sequence of characters enclosed in double quotes, such as "Hello, World!".

When a C program is compiled, the compiler breaks down the program into a sequence of tokens, which are then analyzed and interpreted according to the rules of the language. This process is known as lexical analysis or tokenization. The tokens are then combined into expressions and statements, which are further analyzed and translated into machine code.

In summary, tokens in the C programming language are the building blocks of a program, which are recognized and processed by the compiler. Tokens include keywords, identifiers, operators, punctuation symbols, and literals and are used to define the structure and syntax of the program.