Definition:Minor of Determinant

Definition
Let $\mathbf A = \sqbrk a_n$ be a square matrix of order $n$.

Consider the order $k$ square submatrix $\mathbf B$ obtained by deleting $n - k$ rows and $n - k$ columns from $\mathbf A$.

Let $\map \det {\mathbf B}$ denote the determinant of $\mathbf B$.

Then $\map \det {\mathbf B}$ is an order-$k$ minor of $\map \det {\mathbf A}$.

Thus a minor is a determinant formed from the elements (in the same relative order) of $k$ specified rows and columns.

Also see
The equivalent term in the context of a matrix is a submatrix.