DAPPs are so-called decentralized applications.
DAPPs contain smart contracts.
Why smart contracts?
Imagine having a method available to do things without depending on institutions you can’t trust?
Donations that arrive where you are supposed to because the corresponding token can only be spent where it is meant to be spent….
Supply chains that automatically make payment to the supplier when the medicine is delivered in the correct condition (e.g. temperature measurement in the coin container)….
A currency where the owners decide how to deal with the value (taxes) and not a few…
This means that with Ether, for example, unlike Bitcoin, as a digital currency, you can not “only” receive, own & send, but (as already happened during digitalization with communication, music, film, etc.) you can also program something “on it”. In the EVM.
The Ether Virtual Machine.
One can program Smart Contracts with Solidity (Google it) & thus develop DAPPS e.g. for DeFi (Lending, Funding, YieldFarming).
One can therefore consider Ethereum (whose currency is called Ether), as a 2nd generation Blockchain project.
Cardano also runs on its own blockchain. DAPPs will run on Cardano (only) from February 2021.