Formally, an element of a vector space. An array of order 1.
Mostly, that doesn’t help very much.
As a practical matter, a simple list of scalar-valued data (usually numeric) in which their position in the list denotes some particular meaning of relevance to the user. Different combinations of values (in the various positions in the list) have different implications to that user. That is, the combination connotes information beyond the aggregate of that which is conveyed by the individual elements.