The first time I think I ever heard the word was with one of Stallone's blockbuster movies of the same name. So I just associated it with dangerous situations, especially in rock climbing.
But there is more to CLIFFHANGER than hanging on an edge. Look at definition #3.
from The Free Dictionary
And here's proof to the definition
Remember: if you are talking about a dispute or contest whose final result is totally unpredictable, making the situation one of high tension and extreme suspense, you could say it was a real "cliffhanger".