In what situations should the undefined type be used in TypeScript?

In TypeScript, the undefined type is used to denote variables or properties that are explicitly not assigned a value. It is used in the following situations:

• When a variable may be uninitialized.
• To indicate the absence of a value other than null.
• In functions that may not return a value (for example, returning void or undefined).
• When working with optional parameters or properties that may be missing.

Example:

function greet(name?: string): string {
  if (name === undefined) {
    return "Hello, guest!";
  }
  return `Hello, ${name}!`;
}

Here, name can be undefined if the argument is not provided.