A mathematical array is a list of lists, or a rectangular arrangement of objects; it is a useful way of keeping a collection of things. Arrays are orderly arrangements of objects in columns and rows, with the objects most often being numbers. For example, the most common arrays are two dimensional with a certain amount of rows and columns:

In this case, this is a 2-by-3 array (rows are always mentioned before columns). The order of numbers and/or elements in an array may sometimes, but not always, be significant (as it is in a matrix; see below).