I don't understand what is meant by Falsifiable the way it is used for scientific theory. It's a term that’s usage here is new to me. It doesn't seem to be the same meaning I get from the Webster Dictionary. Could someone explain the difference, or am I just too old and dense? How does being falsifiable make a theory more valid? It would seem that a theory that is not falsifiable would be better.

Falsifiable:
1 : to prove or declare false
2 : to make false : as a : to make false by mutilation or addition <the accounts were falsified to conceal a theft> b : to represent falsely : MISREPRESENT
3 : to prove unsound by experience
intransitive senses : to tell lies : LIE