http://www.livescience.com/21491-what-is-a-scientific-theory-definition-of-theory.html

A scientific theory is a specific type of theory used in the scientific method. The term "theory" can mean something different, depending on whom you ask.

"The way that scientists use the word 'theory' is a little different than how it is commonly used in the lay public," said Jaime Tanner, a professor of biology at Marlboro College. "Most people use the word 'theory' to mean an idea or hunch that someone has, but in science the word 'theory' refers to the way that we interpret facts."
The process of becoming a scientific theory

Every scientific theory starts as a hypothesis. According to the Merriam-Webster Dictionary, a hypothesis is an idea that hasn't been proven yet. If enough evidence accumulates to support a hypothesis, it moves to the next step — known as a theory — in the scientific method and becomes accepted as a valid explanation of a phenomenon.

Tanner further explained that a scientific theory is the framework for observations and facts. Theories may change, or the way that they are interpreted may change, but the facts themselves don’t change. Tanner likens theories to a basket in which scientists keep facts and observations that they find. The shape of that basket may change as the scientists learn more and include more facts. "For example, we have ample evidence of traits in populations becoming more or less common over time (evolution), so evolution is a fact but the overarching theories about evolution, the way that we think all of the facts go together might change as new observations of evolution are made," Tanner told Live Science.

Theory basics

The University of California, Berkley defines a theory as "a broad, natural explanation for a wide range of phenomena. Theories are concise, coherent, systematic, predictive, and broadly applicable, often integrating and generalizing many hypotheses."

Any scientific theory must be based on a careful and rational examination of the facts. Facts and theories are two different things. In the scientific method, there is a clear distinction between facts, which can be observed and/or measured, and theories, which are scientists’ explanations and interpretations of the facts.