Many cryptocurrencies are built on blockchain technology, which is a distributed ledger enforced by a distributed network of computers. Cryptocurrencies are distinguished from fiat currencies like the United States dollar or the British pound because any central authority does not issue them, making them potentially impervious to government intervention or manipulation.
All the signs, however, were there. Like previous bubbles, people were basing their belief in the cryptocurrency on their emotions, not any intrinsic value. Then there was the FOMO element, which only compounded things. Essentially, bitcoin became an international fever. Random companies were “pivoting to blockchain” for no apparent reason other than that it seemed like a way to create buzz. But when the bubble bursts, FOMO turns into fear of losing, which makes for an especially rapid plunge.

Cryptocurrency exchanges play a valuable role in creating liquid markets for popular cryptocurrencies and setting their value relative to traditional currencies. You can even trade cryptocurrency derivatives on certain crypto exchanges or track broad-based cryptocurrency portfolios in crypto indexes.
Crypto coins use the process of mining and the resulting blockchain as a physical measure of the currency. This is similar to how Reserve Banks used to have gold reserves that backed their fiat currencies.