In everyday use, the word "theory" often means an untested hunch, or a guess without supporting evidence.But you only hear this from those promoting biological evolution or climate change theories. Here is more typical scientific usage, from a recent Nature magazine podcast:
But for scientists, a theory has nearly the opposite meaning. A theory is a well-substantiated explanation of an aspect of the natural world that can incorporate laws, hypotheses and facts. The theory of gravitation, for instance, explains why apples fall from trees and astronauts float in space. Similarly, the theory of evolution explains why so many plants and imals—some very similar and some very different—exist on Earth now and in the past, as revealed by the fossil record.
Theories is the right word for it, because no one is really sure. ... Recently there has been a new theory. ... two existing theories... [2:30]That's right, scientists talk about competing theories all the time, and they certainly aren't all well-substantiated as they usually contradict each other.
There are also theories like String Theory, which have no substantiation, and do not even make any testable predictions.
Wikipedia is dominated by evolutionists and climate leftists who insist on defining:
In modern science, the term "theory" refers to scientific theories, a well-confirmed type of explanation of nature, made in a way consistent with scientific method, and fulfilling the criteria required by modern science. Such theories are described in such a way that scientific tests should be able to provide empirical support for it, or empirical contradiction ("falsify") of it. Scientific theories are the most reliable, rigorous, and comprehensive form of scientific knowledge, in contrast to more common uses of the word "theory" that imply that something is unproven or speculative (which in formal terms is better characterized by the word hypothesis).No, the theories on that Nature podcast are not well-confirmed, and String Theory is not described in a way to make it testable.
In Mathematics, a theory is a body of axioms, along with the theorems deducible from those axioms. They are usually computable and consistent, but may not match anything in the real world.