No, it's the "best" possible explanation of observations.
No this is simply wrong. Look it up if you don't believe me. As a quick example we have more than 1 theory of gravitation. That would not be possible if something could only qualify as a theory if it were the best explanation.
If your explanation fits the evidence and can be falsified then chances are it is a theory. It doesn't have to be "the best" (whatever that means) relative to all other possible explanations in order ot qualify as a theory.
Here is what Wiki has to say: "A scientific theory is a well-substantiated explanation of some aspect of the natural world, based on a body of knowledge that has been repeatedly confirmed through observation and experiment."
See, no mention of it having to be the best explanation. Sorry mate but you are wrong here. At least you have learnt something.
However you left out a crucial part - observation AND experiment.
All experiments are performed for the sole purpose of obtaining one or more observations in a controlled environment. So no, you are wrong again.
An experiment with no observation is entirely useless. Even pilot studies have an observation: the methodology works.
The reason you would perhaps mention experimentation with regards to a definition of theories is that you can't get reliable observations without some sort of experiment. So a theory RESULTS FROM observation, experimentation and a dash of creative thinking to put all the pieces we have together to form a coherent picture, but what it explains is the evidence, the observations.
Replicating common ancestral evolution is impossible. Yet, the scientific community is convinced that this is fact.
That view merely explains the evidence mate. It is the theory, not the fact.
EDIT: anyway we are wandering off topic here. I hope this has helped you to better understand what constitutes a valid scientific theory. If not please research it as it is something I feel all human beings should understand.