An ArrayList is a resizable array implementation in the Java programming language that allows you to store a collection of objects. Unlike regular arrays, which have a fixed size, an ArrayList can grow and shrink dynamically as you add or remove elements. This makes it a flexible choice for managing lists of data. You can access elements in an ArrayList using an index, similar to arrays, and it provides methods for adding, removing, and searching for items. The ArrayList class is part of the Java Collections Framework, which offers various data structures to handle groups of objects efficiently.