# Basic Concepts

#### Resource

A resource is an entity that you can use in OTC such as Elastic Cloud Server (ECS), Elastic Volume Service (EVS) disk, Virtual Private Cloud (VPC), etc.

#### Resource Relationship

A resource relationship indicates how your resources in OTC are associated, for example, EVS disks attached to ECSs and ECSs contained in VPCs.

For details, see Relationships with Supported Resources.

Parent topic: Service Overview