Is xy=21 linear or nonlinear

Xy=21 is nonlinear.

I think that because the definitions for nonlinear are:

not denoting, involving, or arranged in a straight line.

and

of or denoting digital editing whereby a sequence of edits is stored on computer as opposed to videotape, thus facilitating further editing.

I believe xy＝21 is nonlinear.

An example of a linear equation would be, y＝5x+4 or 7x＝8+2y.