It means that the writer misspelled “of” as “off”.
The asker is quoting a data dictionary.* The data dictionary lists the name of each field and what it contains. The field in question (the
services field) contains a
Listing *off registered services (nova-scheduler, nova-compute and so on) and their current state.
This is awkward, and as soon the extra f is removed, the awkwardness is gone. The field then contains a
Listing of registered services (nova-scheduler, nova-compute and so on) and their current state.
Others have pointed out that to list off is a verb phrase meaning to recite from a list. This is quite true. But in this context a verb phrase makes no sense. In a description of what a field contains, you expect an object (a list), not a verb (to list).
Still, I suppose it is possible the author intended that the field contains the result when you list off, what you might describe as a listing-off. But then you need the hyphen, and you still need the word of to connect it to the rest of the sentence: the field contains a
Listing-off of registered services (nova-scheduler, nova-compute and so on) and their current state.
If the OP is still in doubt of what was intended I suggest contacting the author.
* The excerpt is taken from the O’Reilly nutshell handbook Deploying OpenStack.