Resource pools explained
In vSphere, resource pools can be used to partition the CPU and memory resources of ESXi hosts or DRS clusters. Resource pools are created as objects on standalone hosts (or clusters) to hierarchically partition available CPU and memory resources. Each resource pool can have shares, limits, and reservations specified.
Resource pools offer a convenient way to separate resources along requirements and control the resource usage of multiple virtual machines at once. For example, you could create two resource pools: the Production resource pool and the Test resource pool and place your production VMs and test VMs accordingly. You could then give higher-priority access to the Production resource pool, in the case of contention.
Resource pools are hierarchically organized. Each ESXi host or DRS cluster has an hidden root resource pool that groups the resources of that host or cluster:
In the picture above you can see that the root resource pool 192.168.5.116 contains two child resource pools: Another example RP and Example RP.