The Stacks blockchain API allows you to query the Stacks blockchain and interact with smart contracts. It was built to maintain paginated, materialized views of the Stacks Blockchain.
The Stacks Blockchain API is hosted by Hiro. Using it requires you to trust the hosted server, but this API also provides a faster development experience. You may wish to consider running your own API instance to create a fully trustless architecture for your app.
You can learn about Stacks blockchain API architecture here.