A
theory is a causal chain, or statements of a causal chain, which have been proven
logically/
mathematically to be true. In other words, a statement is made about a
causal relationship ("X because Y" or "X therefore Y") and that statement is
tested. Evidence is gathered and presented regarding the statement, and evaluated; this might include the results of
observation or
experiment, but in all cases evidence must be grounded in the objective, external world.
A hypothesis is an unproven theory - e.g. it is a statement of a causal chain or relationship, perhaps (one hopes) including an explanation of why it is likely to be true. It has not, however, been subject to definitive or rigorous testing! If I stated "The sky is blue because blue dye evaporates the fastest and humans have made lots of dye in their history so that the sky is permeated with predominantly blue dye," that's a hypothesis.
Although no-one is under any obligation or onus to get these right, if you're serious about your discussions, it is very difficult to have a conversation about science, reality, or even philosophy unless this convention is adhered to by all parties. Otherwise, the conversation degenerates into metasyntactic semantics.