A system of representing a matrix by a symbol is called representation of a matrix.
A matrix with its elements are expressed in matrix form by using either square or round brackets.
It consumes more time to express any matrix more times in mathematics. Instead, matrices are represented by the symbols. Matrices are usually denoted by symbols such as alphabetic letters and etc.
Therefore, consider a letter and equate it to the matrix.
Now, just write the alphabetic character instead of writing the entire matrix in the matrices system of mathematics.