MicroBitcoin (uBTC)

A Ponzi scheme is also referred to as pyramid scheme, and typically takes the form of an investment scheme which pays existing investors with funds collected from new investors.

Decentralized Finance (DeFi) refers to the movement of building decentralized financial applications that have no central authority and is censorship free.

Secondary payment channel occuring off-chain

It is a software that acts like an intermediary or a bridge that lets two applications talk to each other. It is the one that lets applications, data and devices interact.