An array is a data structure that stores a collection of items, typically of the same type, in a fixed-size format. Each item in an array can be accessed using an index, which is a numerical value that indicates the item's position. Arrays are commonly used in programming languages like Python, Java, and C++ to organize and manipulate data efficiently. Arrays can be one-dimensional, resembling a list, or multi-dimensional, resembling a table or grid. They are useful for tasks such as sorting, searching, and performing mathematical operations on large sets of data. The simplicity and speed of accessing elements make arrays a fundamental concept in computer science.