A subdivision of a virtual network that segments resources by IP range for security, organization, and routing control. Used across all cloud providers: AWS subnets within VPCs, Azure subnets within VNets, GCP subnets within VPC Networks, and OCI subnets within VCNs. Like dividing a building into floors with different access rules.
A three-tier application uses public subnets for load balancers, private subnets for application servers, and isolated subnets for databases - each with different security group rules.
A range of IP addresses within a VPC used to organize and secure resources.