I disagree with the dictionary definition ("reasonable or probable") that others have quoted. It is wrong. One danger of the internet is that it gets everyone looking at the same thing, which is unfortunate if the thing they are looking at is wrong.
"Plausable" does not mean "probable". Reasonable yes, but probable no.
A plausible explanation is one that that might very well be correct. It is possibly correct. There is room for it to be correct. However, it need not be probable or likely. In fact, it can be unlikely. Here is the Merriam-Webster definition, which is much better. Notice that under this definition, a plausible explanation can be specious, nearly the opposite of probable:
1 superficially fair, reasonable, or valuable but often specious
a plausible pretext
2 : superficially pleasing or persuasive
a swindler … , then a quack, then a smooth, plausible gentleman
— R. W. Emerson
3 : appearing worthy of belief
the argument was both powerful and plausible