Simple definition
A VMkernel adapter provides an IP interface on an ESXi host for management, vMotion, or storage services.
Purpose and use
A VMkernel adapter supplies a network interface used by ESXi host services.
How does it work?
Depending on configuration, it can carry management, vMotion or selected storage traffic.
Example and verification
Check addressing, VLAN, enabled services, routing and physical uplinks.
Points to watch
It is not a VM’s network adapter. An active physical link does not prove reachability of its associated service.
In short
Test a VMkernel interface in the context of the service it carries.