The document discusses strings and character arrays in C language. It defines strings as a group of characters enclosed in quotation marks and notes that strings are implemented as character arrays in C, with each character occupying 1 byte of memory and the string terminated with a null character. It provides examples of declaring, initializing, reading, displaying and manipulating strings using various string functions like strlen(), strcpy(), strcmp(), strcat(), strrev(), strlwr(), strupr() etc. It also gives programs to demonstrate the use of these string functions.