Minimum height of an official waterfall

This post was in response to What Types Of Waterfalls Are There?

What is the minimum height necessary to say that a waterfall is an official waterfall? I was watching a documentary about Yellowstone Park that said a waterfall has to be a minimum height, and I can’t remember what they said. I think park ranger said it has to be 15 or 30 feet, minimum, to be a waterfall. Not sure if this is true. Is there an official minimum height for a waterfall to be a waterfall??