Yes, Defi is decentralized finance. Which binds crypto currency and finance in the same pair. Bitcoin is a member of defi. Defi's decentralized application allows Bitcoin users. So there is a lot of trade. Which is the new invention of cryptocurrency.
People will get interest, profits, trading money, lend money from their Bitcoin investment via DeFi. Today people not only relate with bitcoin, they also interest with Ethereum, Ripple, EOS, stellar, Tron...