Blow-Off Top
A steep and rapid increase in price followed by a steep and rapid drop in price. 
Here is an example of a blow-off top, a steep rise followed by a steep fall.
Investopedia Commentary
The rapid increase can be a result of either actual news or simply a wild rumor.
Related Links
Why Do Markets Move?
The Uses And Limits Of Volatility
See also: Bear Market, Bull Market, Market Sentiment, Panic Buying, Panic Selling, Pump and Dump, Technical Analysis, Trend, Volatility