Flipenning refers to a circumstance in which the overall market cap of Ether exceeds the total market value of Bitcoin.
During the 2017 bull run, when Ethereum reached an all-time high against Bitcoin, the name was coined.
During the 2017 bull run, the market bet on Ethereum's enhanced flexibility in terms of building applications based on smart contracts. The flood of liquidity caused a significant increase in the price of Ethereum, however its market capitalization ultimately fell in comparison to Bitcoin. At the time of writing, Bitcoin is still the most valuable cryptocurrency in terms of market capitalization, with Ethereum coming in second.

The term "flipping" in the crypto space refers to a hypothetical event where the market capitalization of one cryptocurrency surpasses that of another, leading to a shift in their rankings. The most commonly discussed flipping involves Bitcoin and Ethereum. If Ethereum were to surpass Bitcoin in market cap, it would be considered a significant milestone and could indicate a shift in dominance within the crypto industry.

The concept gained traction as Ethereum's programmability and smart contract capabilities attracted developers and users to its platform. Proponents argue that Ethereum's potential applications go beyond those of Bitcoin, leading to speculation about the flipping. However, as of my last knowledge update in January 2022, Bitcoin has maintained its position as the dominant cryptocurrency by market capitalization. The crypto landscape is dynamic, and the flipping remains a topic of interest and debate among enthusiasts and analysts.