In scientific discussions in the media the media and even in some scientific publications, words such as theory, fact or hypothesis are often used in ill-defined or even confusing ways. Let me try to show some of the differences between common usage and scientific usage of some of these terms.

1. Fact:

scientific	colloquial
An (experimental) observation which has been made repeatedly and in different places by different people. A reproducible observation.	Truth.

2. Hypothesis:

scientific	colloquial
An (often formalized) idea of limited explanatory value derived from multiple scientific facts which is often used to predict future observations which are then attempted in order to test the hypothesis.	Hunch.

3. Theory:

scientific	colloquial
A mathematical or logical explanation of a large number of facts, incorporating a considerable number of tried and tested hypotheses. Often experimentally tested for several decades if not centuries. Nevertheless, every scientist realizes that even scientific theories only remain true until a better theory comes along.	Different from practice.

In this light, it is painful to read in a magazine such as Nature:

Evolution is a tried and tested theory such as Einstein's theory of relativity.
The evolution of land animals from sea-animals is a scientific fact, similar to that of the existence of atoms or the earth orbiting the sun.