Each of the values in an index corresponds to one [[axis]] of the indexed array. When considered in isolation, one of these values (a [[scalar]] number) is called an index ''along'' the corresponding axis. Selecting from the array using this index produces an array whose [[rank]] is one smaller than the initial array (and it cannot be done to a [[scalar]], as there are no axes along which to index). This array is sometimes called a "slice" or [[hyperplane]] of the array. Selecting on the first axis gives a [[major cell]], one kind of hyperplane.
The set of possible indices into an array as a whole is the [[wikipedia:Cartesian product]] of the possible indices into each axis.
== Index of a cell ==