What is an array?

An array is defined as a collection of items stored at contiguous memory locations, which is fundamental to understanding how arrays work in various programming languages. This means that the elements of an array are laid out sequentially in memory, allowing for efficient access and manipulation of data. When you know the starting address of an array, you can calculate the address of any element by using its index, which facilitates fast retrieval and modification of its contents.

Other choices describe different data structures or characteristics. The first choice refers to a tree structure, which implies hierarchical organization rather than linear, contiguous memory. The second option hints at a single variable holding multiple values, which can be misleading since arrays are specifically about the orderly placement and access of those values, not merely storing multiple values as a single entity like in list or set types. The last choice suggests a list with no fixed size, which more closely aligns with dynamic data structures such as linked lists or other flexible collections rather than the fixed-size nature of an array in many programming scenarios.