With vApps, you can combine multiple VMs into a single unit. vApps are represented as objects in the vCenter Server inventory and can be managed as any other virtual machine (powered on, powered off, cloned, etc.).
Why would you use a vApp? Well, today’s enterprise applications are rarely constrained to a single VM and usually have components spread across multiple VMs. For example, you might have a front-end web server running on one virtual machine, an application server running on another VM, and a backend database server running on yet another VM. Because these components have certain dependencies (such as a specific start order), you can use vApps to combine multiple VMs into a single unit and manage them as such.
You must have vCenter Server installed in order to create vApps. A vApp is represented as an object in the Hosts and Clusters view: