What is the difference between ultraviolet light and ordinary light?

They are both names given to a range of frequencies of electromagnetic waves. Ultraviolet light is a higher frequency, and shorter wavelength, than the range which human eyes perceive as visible light. There are animals who "see" in that range, but we are not one of them.

https://earthsky.org/space/what-is-the-electromagnetic-spectrum

So far as the universe is concerned, none except for wavelength. Visible light is what we humans can see; ultraviolet is off the scale to the left, and infrared is off to the right. No magic involved - no physical boundary either. Some humans can see more towards ultraviolet, others more towards infrared. In theory, it ought to be possible for some sort of creature (possibly looking like the one that can be made out in the box containing the word 'Electromagnetism' in the reference below) to see in any part of the electromagnetic spectrum. Another diagram on that page (below a load of maths) shows just how small a part we use (with our eyes, that is). What other colours would look like is more a matter for science fiction (bees can see in ultraviolet, but they are keeping shtum on what it looks like, and Terry Pratchett's description of octarine as a sort of greeny-yellow purple doesn't really help either). Possibly it would not be possible to describe other colours in terms we could understand - how can you describe a colour to a blind from birth person? https://en.wikipedia.org/wiki/Electromagnetic_radiation and also https://en.wikipedia.org/wiki/Visible_spectrum