What is defined as an 'array' in programming?

An 'array' in programming is best defined as a collection of items stored at contiguous memory locations. This characteristic is fundamental to how arrays operate, as it allows for efficient access to the elements within the array through indexing. Each element can be accessed directly using its index, which is a numerical representation of its position within the array.

Arrays enable storage of multiple values of the same type, neatly packing them together in memory. This organization is crucial for algorithms that require processing lists of data efficiently, as the contiguous layout also enhances performance by leveraging cache memory effectively.

The other options represent different concepts in programming. The notion of a dynamic set of items pertains more closely to data structures like lists or collections that can grow or shrink in size, while variables that hold multiple types of data refer to structures like tuples or dictionaries in certain languages. Storage of key-value pairs specifically describes associative arrays or hash maps, which have different organizational principles compared to traditional arrays.