A programming language used in object-oriented programming. In such a system the concept of procedure and data, which is embodied in conventional programming systems, is replaced by the concepts of objects and messages: an object is a package of information and a description of its manipulation, and a message is a specification of one of an object’s manipulations. Unlike a procedure, which describes how manipulations should be carried out, a message merely specifies what the sender wants done, and the receiver determines exactly what will happen. See also C++, Smalltalk.