The determinant is specific scalar value (a single number)
Only applies to square matrices. Otherwise the determinant D.N.E
It's denoted by various symbols, including , , or .

Singular Matrix

A matrix is called "singular" if its determinant equals 0. This also implies that the matrix has no inverse.

Calculating a Determinant

Determinant of a 1x1

Determinant of a 2x2

Determinant of a 3x3

Hint

If the matrix is in Upper Triangular Form then you can just multiply the diagonal values together.