This service is associated with EC$2$ instances and provide security at the protocol and port access level. Each one contains a set of rules that filter traffic coming into and out of an EC$2$ instance. If there is no rule that explicitly permits a particular data packet, it will be dropped. They also can be applied to many other services within your VPC$,$ including ELB, RDS$,$ Redshift, ElastiCache, and others.