Api Gateway is a service in AWS that allows creating apis that can call other http apis or call lambda functions. This helps in building a serverless architecture where for example, a website can be hosted in S3, that calls apis in Api Gateway which calls lambda functions that interacts with a database. The apis can be cached, monitored and logged and can have custom domain name. The apis can also be behind authorisation
The Api Gateway provides a robust, secure, and scalable mobile and web application backends and the helps the developers to create application without having to deploy any servers. This is great and reduces the system overheads and the developers can solely work on the business logic for getting the api working.