The key configuration is very flexible, but to complex for the end user. The admin can provide these templates so that the user only needs to select a function for a key and enter a few necessary parameters.
A template predefines an key setup and specifies the needed parameters.
Since the templates are part of the phones configuration, they can be provided via provisioning. One can for example choose to change the inner workings of a key-function. E.g. you can overwriting the local call-forward toggle by provisioning a call forward-template that is designed to toggle call forwarding in our pbx.
The phone when first installed (or after settings-reset) comes with a list of available functions to choose from when setting up a key. Actually there are 2 lists: You can add a second set of functions by selecting "activate vendor templates" in the provisioning-subsection of the settings-menu on the phone.