Why edge sharpening produces high frequency?

1. Why are edges high frequency?
2. What is edge sharpening in image processing?

Why are edges high frequency?

I have read somewhere that edges are regions of the image where the intensity changes rapidly, so that's why it's high frequency. The way I understand it is: High frequency implies rapid change.

What is edge sharpening in image processing?

Edge enhancement is an image processing filter that enhances the edge contrast of an image or video in an attempt to improve its acutance (apparent sharpness).