A dapplet is an application that runs on top of various web pages in a browser. It can insert useful widgets, buttons, add new functionality, create absolutely new user scenarios, and change the usual experience of interacting with familiar web resources.
The key factor is that you don't have to be a YouTube or Twitter developer to add functionality that you thought was missing for so long or is relevant right now. Or maybe someone has already implemented it? Then it’s easy enough to find and enable the corresponding dapplet!
The name dapplet consists of two parts: dapp and applet. Dapp is a decentralized application. The code of all dapplets is stored on the blockchain, as are dapplet registries, which are smart contracts with information about published dapplets, their owners, and the contexts in which they operate.
Decentralization provides such advantages as ownership of your own data and the security of their storage, transparency of transactions, absence of censorship, accessibility, reliability and many others.
An applet is an application that exists in the context of another, larger web application and performs a specific task. Dapplets do not exist separately from the contexts for which they are written. They can be said to mutate or augment existing popular resources.