The massive run up in prices is reserved by a quick decrease in value. This contraction is notable because of the speed and force with which it takes place.
In equities, bubbles can occur when stocks far exceed their "fundamental value". This can be defined as the present value of the stream of payments the shareholder expects to receive. This is a combination of the dividends expected to receive along with the anticipated sales price at some future date.
When markets are efficient, this value will equal the stock price. A bubble results when prices exceed this level, often by a large margin.
- Profit Taking
Probably the most famous could be Tulip Mania in the 1600s where people paid insane prices for tulips.