In science, a theory is “a well-substantiated explanation of some aspect of the natural world that is acquired through the scientific method and repeatedly tested and confirmed”–according to Wikipedia. This is frequently contrasted with the colloquial meaning of “theory”, which usually refers to something speculative and unconfirmed. It is suggested that in a scientific context, it is more appropriate to refer to a speculative idea as a “hypothesis”.
However, in my experience as a physicist, this is not how the word “theory” is used in practice. Generally, the word “theory” is contrasted with “experiment”, describing the kind of work rather than the quality of the work. Since theories are carefully crafted by experts, it is fair to say that they are more than mere speculation, but that doesn’t mean that every theory has been thoroughly tested and confirmed. Some theories are untested, some theories are in direct competition with other equally viable theories, some theories intentionally model things that do not presently exist, and some theories are just poorly crafted.
So, basically, Wikipedia–and most dictionaries as well–appear to be in conflict with my understanding as a fluent speaker of English physics. That probably means there’s some bad lexicography going on.