An ArrayList is a dynamic data structure in many programming languages, such as Java, that allows for the storage of an ordered collection of items. Unlike arrays, which have a fixed size, an ArrayList can grow or shrink dynamically as elements are added or removed. This makes it a more flexible alternative for handling collections of data that may change during program execution.

Definition: An array list is a data structure that stores elements in an ordered collection and allows dynamic resizing. It can grow and shrink as elements are added or removed.

ArrayLists are similar to arrays in that they allow for the quick access of elements via indices. However, the advantage of an ArrayList is its ability to resize itself automatically when elements are added or removed. For example, in Java, the ArrayList class provides methods like add(), remove(), and get() to manipulate and access data, while ensuring efficient memory management behind the scenes.

ArrayLists are particularly useful when the size of the collection cannot be determined ahead of time or when the collection is expected to change frequently. However, they may not be the best choice for scenarios requiring fast access to large amounts of data, as resizing operations can be time-consuming.