The slang "DeFi degens" is covered in the entry Degen, which explains where the word comes from, how it is used and the behaviour it describes. This page gives a short definition and explains why the longer phrase exists.
DeFi degens are participants in decentralized finance who take on unusually high risk in search of quick gains. Typical behaviour includes moving money into brand-new protocols as soon as they launch, chasing very high advertised yields through yield farming, borrowing heavily to multiply positions and buying newly listed tokens within minutes, a habit known as apeing. Many degens accept that some protocols will fail or be exploited and treat their activity as a form of high-stakes speculation rather than investment. The term is often used with self-mocking humour within crypto communities, but the risks are real: unaudited contracts, sudden token collapses and outright scams can wipe out funds, a result described by the slang rekt.
"Degen" is short for "degenerate", borrowed from gambling slang. Adding "DeFi" simply specifies the setting, as opposed to degens who trade memecoins or leveraged futures on centralized exchanges. Both phrases describe the same attitude, so this site keeps one main entry.