The software that actually runs containers on a computer, managing their lifecycle from creation to deletion. Like the engine that powers and manages each container.
Docker Engine and containerd are popular container runtimes that Kubernetes uses to start, stop, and manage containers on servers.
A container runtime is not a managed cloud service; it’s node-level software (for example, containerd or CRI-O) installed on servers/VMs that runs containers. Managed Kubernetes offerings (like EKS/AKS/GKE/OKE) include and manage a runtime on worker nodes, but the runtime itself is not a standalone cloud service you purchase.