Codility:
An array is an abstract data type:
In computer science, an abstract data type (ADT) is a mathematical model for data types. An abstract data type is defined by its behavior (semantics) from the point of view of a user, of the data, specifically in terms of possible values, possible operations on data of this type, and the behavior of these operations. This mathematical model contrasts with data structures, which are concrete representations of data, and are the point of view of an implementer, not a user.
Formally, an ADT may be defined as a "class of objects whose logical behavior is defined by a set of values and a set of operations".
Array definition on Wikipedia:
In computer science, an array type is a data type that represents a collection of elements (values or variables), each selected by one or more indices (identifying keys) that can be computed at run time during program execution. Such a collection is usually called an array variable, array value, or simply array.[1] By analogy with the mathematical concepts vector and matrix, array types with one and two indices are often called vector type and matrix type, respectively.