A substring is a smaller sequence of characters that is part of a larger string. For example, in the string "hello world," the substring "hello" consists of the first five characters. Substrings can vary in length, ranging from a single character to the entire string itself. They are commonly used in programming and text processing to search, manipulate, or analyze text data. In many programming languages, such as Python or Java, there are built-in functions to extract substrings easily. These functions allow developers to specify the starting position and length of the substring they want to create. Understanding how to work with substrings is essential for tasks like data validation, text formatting, and searching for specific patterns within strings.