In this context, this means running K8s nodes directly on the hardware.
As opposed to running the nodes as virtual machines. Normally VMs are used in the context of cloud providers but it's not uncommon (with beefier hardware) to run k8s as VMs in datacenters. Deployments on top of OpenStack, Azure Stack or Anthos are common. As is ESXi. It's another abstraction layer, but that gives you easier handling of things like storage and, in some cases, networking.
> More recently, the definition has confusingly expanded to sometimes include an operating system, but without a hypervisor.
In this context, this means running K8s nodes directly on the hardware.
As opposed to running the nodes as virtual machines. Normally VMs are used in the context of cloud providers but it's not uncommon (with beefier hardware) to run k8s as VMs in datacenters. Deployments on top of OpenStack, Azure Stack or Anthos are common. As is ESXi. It's another abstraction layer, but that gives you easier handling of things like storage and, in some cases, networking.
> More recently, the definition has confusingly expanded to sometimes include an operating system, but without a hypervisor.
That's exactly it - the definition has expanded.