Market bubbles are covered in full in the entry Economic Bubble, which explains how bubbles form, the stages they pass through, famous historical examples and the debate over whether they can be spotted in advance. This page gives a short definition and explains the different names.
A bubble is a period in which the price of an asset, such as shares, property, commodities or cryptocurrencies, rises far above any reasonable estimate of its underlying value, driven by optimism, easy credit and the expectation that prices will keep rising. Buyers increasingly purchase because others are buying, a pattern linked to the bandwagon effect and studied in behavioral finance. When confidence breaks, prices can fall quickly, sometimes triggering a wider financial crisis. Crypto examples are discussed in crypto bubble.
"Bubble", "market bubble", "asset bubble", "speculative bubble" and "economic bubble" are all used for the same phenomenon. The choice of word often depends on context: traders tend to say "bubble" or name the asset, as in "housing bubble", while economists more often refer to asset or speculative bubbles. A bubble's end is commonly called a crash or bursting, and the cycle as a whole is sometimes described as boom and bust.