A null terminator is a special character used in programming to indicate the end of a string. It is represented by the value `0` and is crucial in languages like C and C++, where strings are often handled as arrays of characters. The null terminator allows functions to determine where the string ends, preventing reading beyond the intended data. When a string is created, the null terminator is automatically added at the end. For example, the string "Hello" is stored as the characters 'H', 'e', 'l', 'l', 'o', followed by a null terminator. This ensures that any operations on the string, such as printing or copying, function correctly without errors.