What is AWS?
AWS stands for Amazon Web Services that provides hardware in cloud environment for your computing needs. Instead of you going to a datacenter and signing up for a contract of 3 to 5 years for all your hardware needs, with AWS you can just get that on-demand without signing any contracts and if your start-up idea didnot work you can just terminate all your servers and only pay for what you have used instead of getting stuck in those contracts.
AWS provides virtual machines instantly with the click of a button. You would pay only for the time the servers were up and running. No more hassle with buying or renting servers under contracts. Startups can quickly bring up their servers, implement their ideas and if something is not working there is very little to loose. That's the beauty of AWS in a nutshell.
AWS has evolved a lot in last 15 years. If you are preparing for AWS Certified Solutions Architect Professional Certification Exam here is more info which helps you remember AWS technologies better.