Simple definition
VMkernel is the core of VMware ESXi responsible for scheduling, memory, storage, and host resource management.
Purpose and use
VMkernel is the ESXi hypervisor kernel, managing resources and services needed to run VMs.
How does it work?
It participates in scheduling, memory, storage and networking alongside other platform components.
Example and verification
For a host incident, distinguish hypervisor events from guest-operating-system events.
Points to watch
A VMkernel adapter is a host-service network interface, not the kernel itself.
In short
Target the affected layer: host kernel, service or guest operating system.