There is no need to provision or maintain any servers. There is no software or runtime to install, maintain, or administer.
Your application can be scaled automatically or by adjusting its capacity through toggling the units of consumption (e.g. throughput, memory) rather than units of individual servers.
Serverless applications have built-in availability and fault tolerance. You do not need to architect for these capabilities since the services running the application provide them by default.
You do not have to pay for idle capacity. There is no need to pre- or over-provision capacity for things like compute and storage. For example, there is no charge when your code is not running.
You can build a serverless web application by using several AWS services together. Each service is fully managed and does not require you to provision or manage servers. You only need to configure them together and upload your application code to AWS Lambda, a serverless compute service.