Explain how to tell weather an event is as likely as not

I think the answer may be that an event is as likely as not to happen when the probability of the event happening is 50%, and the probability of the event not happening is 50%. Like a coin toss, the chance you will flip a "heads" is 1/2 or 50%, and the chance that you WON'T flip a heads is also 1/2 or 50%