Theory

There are two main meanings of the word theory:

• informal theory
  • "a belief, policy, or procedure proposed or followed as the basis of action" (m-w.com), "An unproven conjecture" (wiktionary)
• scientific theory
  • "A coherent statement or set of statements that attempts to explain observed phenomena, which has testable implications, and which is well tested and widely accepted as true." (wiktionary)