VMware vSphere is a virtualization platform that enables users to create, deploy, and manage virtual machines, while VMware vCenter is a centralized management tool that enables administrators to manage multiple vSphere environments from a single console.
In simpler terms, vSphere is the technology that powers virtualization, while vCenter is the tool used to manage and monitor vSphere-based virtual environments. VCenter provides a single place to manage all aspects of virtualization, from creating and managing virtual machines to configuring network and storage resources, setting security policies, and monitoring performance. In contrast, vSphere only provides the basic virtualization functions such as creating, deploying, and maintaining virtual machines.