Matrix addition is a mathematical operation where two matrices of the same dimensions are combined by adding their corresponding elements. For example, if you have two matrices, A and B, both with 2 rows and 3 columns, you add the element in the first row and first column of A to the element in the first row and first column of B, and so on for all elements. The result of matrix addition is a new matrix, C, that also has the same dimensions as the original matrices. This operation is only possible when the matrices have the same size, meaning they must have the same number of rows and columns.