The document discusses unsorted lists as an abstract data type (ADT). It defines an unsorted list as a collection of homogeneous elements in no particular order, where the only relationship between elements is predecessor and successor relationships. The document outlines common operations for an unsorted list ADT like creating and initializing a list, checking if it is empty, finding the size, inserting and removing elements. It also discusses two common implementations of an unsorted list using an array or linked structures.