In programming, "null" or "void" refers to the absence of a value or an object. It indicates that a variable has been declared but does not currently hold any data. This concept is crucial in many programming languages, such as Java, C#, and JavaScript, as it helps developers manage memory and avoid errors when trying to access non-existent data. The term "void" is often used in function definitions to indicate that a function does not return any value. For example, in C++, a function declared with a "void" return type performs its task without sending any information back to the caller. Understanding these concepts is essential for effective programming and debugging.