Conjecture
A conjecture is a opinion and/or theorem that does not have enough evidence for proof.
Some examples of some famous conjectures are the Hodge Conjecture, Poincaré Conjecture, Birch and Swinnerton-Dyer Conjecture, P versus NP, Riemann Hypothesis, Navier-Stokes Equations, Yang-Mills Theory, Goldbach Conjecture, and the Twin Prime Conjecture.