AWS Certified Solutions Architect Associate Test 6

A security group controls the access to a DB instance. It does so by allowing access to IP addressranges or Amazon EC2 instances that you specify.
Amazon RDS uses DB security groups, VPC security groups, and EC2 security groups. In simple terms,a DB security group controls access to a DB instance that is not in a VPC, a VPC security groupcontrols access to a DB instance inside a VPC, and an Amazon EC2 security group controls access toan EC2 instance and can be used with a DB instance.
Reference: http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Welcome.html