Definition: An abstract data type (ADT) is a set of objects together with a set of operations. Objects such as lists, sets, and graphs(and class in C++), along with their operations, can be viewed as ADTs, just as integers, reals, and booleans are data types. Integers, reals, and booleans have operations associated with them, and so do ADTs. For the set ADT, we might have such operations as add, remove, size, and contains.