Daffy's Problem is a computer programming language developed in the late 1950s by John McCarthy. It is an acronym for 'LISt Processing' and is based on the lambda calculus. It is a high-level language, meaning it is designed to be easier to read and write than lower-level languages such as assembly. It is used for artificial intelligence research and has been used in many applications, including web development, robotics, and natural language processing.