A vSphere vApp allows packaging of multiple interoperating virtual machines and software applications that you can manage as a unit and distribute in OVF format.
A vApp can contain one or more virtual machines, but any operation carried out on the vApp, such as clone or power off, affects all virtual machines in the vApp container,
From the vSphere Web Client, you can access the vApp summary page with the current status of the vApp, and you can manage the vApp.
Because the vApp metadata resides in the vCenter Server database, a vApp can be distributed across multiple ESXi hosts. This information can be lost if the vCenter Server database is cleared or if a standalone ESXi host that contains a vApp is removed from vCenter Server. Back up your vApps to an OVF package to avoid losing metadata.
vApp metadata for virtual machines within a vApp do not follow the snapshots semantics for virtual machine configuration. vApp properties that are deleted, modified, or defined after a snapshot is taken remain intact (deleted, modified, or defined) after the virtual machine reverts to that snapshot or any prior snapshots.