You can use the OVF Authoring options that are included in a virtual machine's vApp options to specify custom information that is included when you export the virtual machine as an OVF template.
vApp properties are a central concept of vApp deployment and self configuration; they can turn a general OVF package into a running vApp instance with a custom configuration.
The set of properties associated to a running vApp is determined by the OVF package from which the vApp was deployed.
When an OVF package is created the author adds the set of properties necessary for the vApp to function in an unknown environment. This could for instance be properties containing network configuration, a property containing the email address of the system administrator or a property containing the number of expected users of the vApp.
Some property values are entered by the user when the vApp is deployed, while other property values are configured by vCenter Server when the vApp is powered on. How this is handled depends on the property type and vCenter Server configuration.
When vCenter Server powers on a vApp, it creates an XML document that contains all properties and their values. This document is made available to each virtual machine in the vApp, and allows the virtual machines to apply the properties to their own environment.