What is the difference between ec2 and RDS?

What is the difference between ec2 and RDS?, AWS is all about providing computing infra structure in on demand basis. EC2 and RDS are the 2 different service offerings from AWS. EC2 : Elastic Compute Cloud - On demand Servers either Linux / Windows. By extension to the previous point, you can connect to the RDS from your app running in EC2., AWS Free Tier, AWS