In C programming, a string is a sequence of characters that is terminated by a null character ('\0'). Strings are typically used to represent textual data and are represented as arrays of characters.

Here is an example of declaring and using a string:

#include <stdio.h>

int main() {
  char greeting[] = "Hello, world!"; // declaring and initializing a string
  
  printf("%s\n", greeting); // printing the string to the console
  
  return 0;
}

In this example, we declared a string named greeting and initialized it with the text "Hello, world!". The string is represented as an array of characters, with each character stored in a separate element of the array. The null character at the end of the string marks the end of the string.

To access individual characters within a string, we can use array indexing. For example, greeting[0] would give us the first character of the string, which is 'H'. We can also use string manipulation functions, such as strlen() to get the length of a string, or strcpy() to copy one string to another.

It is important to note that strings in C are not a built-in data type, but are instead represented as arrays of characters. This means that strings in C are null-terminated, which can sometimes cause issues with buffer overflows if care is not taken to ensure that the string does not exceed the size of the buffer.

In summary, a string in C programming is a sequence of characters that is terminated by a null character. Strings are typically used to represent textual data and are represented as arrays of characters. They can be accessed using array indexing or string manipulation functions, but care must be taken to ensure that the string does not exceed the size of the buffer.