In programming, "None" or "Null" represents the absence of a value or a non-existent reference. It is used to indicate that a variable does not point to any object or data. This concept is crucial in various programming languages, such as Python, Java, and JavaScript, where it helps manage memory and control program flow. When a variable is set to None or Null, it can help prevent errors by signaling that no valid data is available. Developers often check for None or Null values to avoid unexpected behavior in their applications, ensuring that the code runs smoothly and efficiently.