What does "evolution remains a theory" mean?Do creationists think scientific theories change to something else?

It remains a theory because there is no experiment that can be done to prove it. That's how we go from theories to facts. Since we don't know the conditions at the beginning of time (whether you say creation or evolution) it is impossible to replicate those conditions. We cannot replicate what we do not know. So, Darwin espoused this theory and it seems to have "stuck". Wide acceptance does not take it out of the realm of a theory, it just means it has wide acceptance.