Without getting too technical, traditional apps are based on what’s known as the “client-server model”. A person uses an app as the “client” which connected to a centralized “server” for processing and other tasks. Think of your favorite email application - the interface you use to compose and send emails is the client portion, where the email delivery is done through the server.
In contrast, a distributed app is both the client and server, broadly speaking. Distributed apps use the “peer-to-peer model,” where an app, connected to other peer apps through a network, coordinates computing tasks without the need for a central server. A familiar example of this computing model might be peer-to-peer file sharing (using Torrent technology), but other innovative applications for this technology have been developed, such as peer-to-peer lending and digital cryptocurrencies (using blockchain).