What is well-defined?

Well-defined means that a concept or mathematical object has a clear and unambiguous definition or meaning. It is important for a concept or object to be well-defined in order to avoid confusion or ambiguity in communication and analysis. For example, a function is well-defined if it always produces the same output for a given input, and a set is well-defined if its membership is unambiguous and clearly defined. In mathematics, well-definedness is essential for rigour and accuracy in mathematical proofs and arguments.