EC2 is short for Elastic Compute Cloud, and it provides scalable computing capacity.

 Using Amazon EC2 eliminates the need to invest in hardware, leading to faster development and deployment of applications. 

You can use Amazon EC2 to launch as many or as few virtual servers as needed, configure security and networking, and manage storage. 

It can scale up or down to handle changes in requirements, reducing the need to forecast traffic.

 EC2 provides virtual computing environments called “instances.”

https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/concepts.html

This is a web service that provides a re-sizable compute in the cloud.

AWS EC2 reduces the time required to obtain and boot new server instances to minutes allowing you to quickly scale capacity, both up and down, as your computing requirements change.

In the old world if you need an app server or DB server, you would first need to talk to your developer, decide the size and number of cores you need, and then talk to your procurement team, and by the time the server is in your data center it could take 2+ months.

Now with EC2, you have this with a click of a button. This also means from a startup perspective you do not have the upfront cost of buying all the hardware you need.

EC2 changes the economics of computing by allowing you to pay only for the capacity that you actually use. You also have several tools at the disposal of the developers to build the applications to be resilient and isolate them from failure scenarios.