All these terms are part of the same family. Part of the difference is just that several people tried to 'coin' a group of new technologies with their own word. Ubicomp was coined by Weiser. His ideas are perhaps the least 'technical' and the most 'philosophical' - internet of things is often used in more popular media with less of a deep theory or idea behind it. I think what Wikipedia says about it pretty much covers it. (And so... there is no exact answer ...)

I think that the concept of IoT is wider and applies to items that ubiquitous computing can use as resources. As Jelle mentions, there is a 'run' to coin each concept as we can perceive by their abundance; web of things, internet of things, internet of everything, etc. Everybody (including media) knows the central region of those concepts but the boundaries are still to be defined.

Please refer to my answer to a similar question here on RG: https://www.researchgate.net/post/are_internet_of_things_pervasive_computing_and_ubiquitous_computing_the_same

In short: UbiComp was designed to make objects intelligent and create richer interaction, the Internet of Things was much more focussed on virtual representations of automatically identifiable objects.