What is cloudlet in CloudSim?

Excuse me, could you please elaborate on the concept of cloudlet within the context of CloudSim? I understand CloudSim is a simulation framework for cloud computing environments, but how does the notion of a cloudlet specifically fit into this picture? Is it a specific type of virtual machine, a resource allocation strategy, or perhaps something else entirely? I'm particularly interested in its purpose, functionality, and how it might impact the simulation of cloud-based services and applications.