A Bubble is a market situation where investors in the market drive prices up above their “real value”. Following that, there is a market price correction where prices drop rapidly. Famous examples of Bubbles is the The Dutch Tulip Bubble (also known as a Tulipomania), 1634-1637 and the Dot.com Bubble (late 1990s). Some people argue that Bitcoin’s price development in Dec 2017-Jan 2018 had bubble-characteristics.