EC2 - Elastic Compute Cloud

Create virtual machines/instances. The size of instances range from micro to 32+ processors with GBs of memory. Instances can be placed in many different regions for redundancy (West Coast, East Coast, Europe, Asia, etc)

IAM - Identify and Access Management

Create Users, Roles, and Permissions

RDS - Relational Database Storage

Create Postgres, MySQL, Maria DB, or Aurora instances. I think of this as a specific type of EC2 instance being created, with a database pre-installed.

VPC - Virtual Private Cloud

Create public or private virtual clouds. Virtual clouds have many virtual containers/boxes/instances.

Public clouds often start with CIDR blocks like 172.30.0.0/24. Private clouds often start with CIDR blocks like 10.0.0.0/16.

Within a VPC is a Subnet. Subnets are use CIDR blocks to define ranges of addresses. Subnets are often used to separate public and private traffic, as well as separate types of machines or processes.