Containers as a Service (CaaS) is a cloud service that manages containers at large scale, including starting, stopping, scaling, and organizing containerized workloads. Examples of CaaS services are Amazon Elastic Container Service (ECS), Amazon Fargate, and Azure Container Instances (ACI).
CaaS are a middle ground between container engines like Docker, which let you manage individual containers without orchestration capabilities, and full-featured orchestrators like Kubernetes, which provide powerful cluster management capabilities, but are complex to setup and maintain.
Within the scope of cloud computing services, CaaS provides more capabilities than Infrastructure as a Service (IaaS), but has less features than most Platform as a Service (PaaS) offerings. CaaS is most commonly deployed in an IaaS model, except that its primary resource unit is containers, not virtual machines (VMs) or bare metal servers.