This tag is for challenges involving matrices. A matrix, also known as a 2D array, is a list of numbers arranged in a rectangle with rows and columns.
In mathematics matrices are often used to represent linear transforms from one vector space to another. If your challenge involves such matrices consider adding the additional tag of linear-algebra.
If your challenge has to do with matrices that can only contain 1s and 0s, consider adding the tag binary-matrix.
For a challenge that isn't relevant to the mathematical properties of a matrix, consider using the tag grid instead.