For any square matrix A;(A-A') is :

$A' \text{ denotes transpose of } A.$

$A-A' = -(A'-A).$

$(A-A')' = A'-A = -(A-A').$

$\text{ therefore } A-A' \text{ is skew-symmetric.}$

$\text{Correct option: Skew-symmetric matrix}.$