science: a way of knowing about the natural world
Scientific explanations are based on observations and facts that can be confirmed or disproved by other scientists using accepted scientific techniques.

law: a description of how a natural phenomenon will occur under certain circumstances
Kepler's Law of Planetary Motion describes the relationship between the time it takes a planet to go around the Sun and the planet's distance from the Sun.

fact: a natural phenomenon repeatedly confirmed by observation
It takes Venus 225 days to go around the Sun.

hypothesis: a possible and testable statement about a natural phenomenon
Newton proposed that the force of gravity between two objects depends on the distance between the objects.

theory: a well-substantiated explanation of some aspect of the natural world that typically incorporates many confirmed observations, laws, and successfully verified hypotheses
Heliocentricism: the Sun is the center of our solar system.

SOURCE: http://www.pbs.org/wgbh/evolution/educators/teachstuds/pdf/unit1.pdf