Final answer:
RDS Read Replicas is the feature in Amazon RDS that scales the system for READ operations, by creating read-only copies to handle read-intensive workloads, and is distinct from Multi-AZ, Snapshots, and Subnet Groups.
Step-by-step explanation:
The feature of Amazon RDS (Relational Database Service) that allows the system to scale for READS is RDS Read Replicas (RDS RR). Read Replicas enable you to have read-only copies of your database instance, which can be used for handling read-intensive database workloads. This effectively scales out read operations and enhances the performance of the system during read-heavy activities. In contrast, Multi-AZ is for high availability and failover, RDS Snapshots are for backups, and RDS Subnet Groups are used for defining subnets within a VPC for RDS deployment.