Three main types of APIs used in Salesforce are-

1. REST API- It allows the user to integrate with applications with the help of simple HTTP methods in JSON or XML formats. This idea is used to develop external clients and mobile applications.

2. Bulk API- it offers programmatic access that makes it easy to load data in the Salesforce organization.

3. Streaming API- When a user wants to receive notifications regarding the changes made in Salesforce data then Streaming API is used. For that, a SOQL query should be defined.

BY Best Interview Question ON 24 Jul 2021