The term Flippening was colloquially coined in 2017 and refers to the possibility of the market capitalization of Ethereum
(ETH) overtaking the market capitalization
(BTC). Therefore, the term describes the hypothetical moment in the future when Ethereum becomes the biggest cryptocurrency
by market capitalization.
The market capitalization (market cap) of a crypto-currency is defined loosely by its circulating supply multiplied by its current market price (although some measures don’t take into account coins or tokens that were lost). Currently, Bitcoin is ranked number one in terms of market cap, followed by Ethereum.
Although BTC has always been the number one cryptocurrency by market capitalization, its market dominance
dropped significantly in recent years. The drop was particular visible in mid-2017 and early 2018. During those periods, many Ethereum supporters were hoping for the Flippening to happen. Speculators were stating that the greater flexibility and the ability to write smart contracts would propel Ethereum over Bitcoin in those rankings, but the Flippening never really occurred.
The Flippening watch website can be used as a reference to track the progress of Ethereum in comparison to Bitcoin.