A null matrix, often called a zero matrix, is a matrix where every element is zero.
Example:
$ A = \begin{bmatrix} 0 & 0 & 0 \\ 0 & 0 & 0 \end{bmatrix} $
The rank of a matrix is the dimension of the vector space formed by its columns (or rows). It signifies the maximum number of linearly independent columns or rows within the matrix.
For a null matrix:
Consequently, the $rank$ of any null matrix is always 0.