Zelle is a money exchange system, that is setup through mobile banking apps. Zelle is to be used between two parties who trust each other, such as family, friends, or coworkers. To start, each party must setup Zelle on their app. From there, the parties can send and request money through each other.
Zelle is an alternative to the many other money exchange systems such as PayPal, CashApp, and Velle. Many prefer Zelle because it is setup exclusively through their bank. Therefore, if something goes wrong they can not only contact Zelle's customer support, but also dispute the charge with their bank.