String concatenation is the process of joining two or more strings together to form a single string. In programming, strings are sequences of characters, such as words or sentences. For example, if you have the strings "Hello" and "World," concatenating them would result in "HelloWorld" or "Hello World," depending on whether you add a space. Different programming languages have various methods for string concatenation. In Python, you can use the `+` operator, while in Java, you can use the `concat()` method or the `+` operator as well. Understanding string concatenation is essential for manipulating text data in software development.