Searching for "rep ability" yields 2 real results, both times used by Jeff Atwood to refer to 20k privileges. With such a meagre result, it seems fair to conclude that its usage never really caught on.
There are already tags covering this, e. g.
- privileges (note that "ability" is a tag synonym)
- trusted-user ("20k" is a tag synonym)
Having a look at the individual questions tagged rep-ability:
1) Moderator abilities
- Implement Ratios For Moderation Abilities (rep-ability doesn't add anything useful, I suggest replace it with moderator-abilities)
- Make Moderator abilities relate to Rep Inflation (already has moderator-abilities and rep-ability can be removed)
- Lost my motivation after 3000 points (I suggest motivation and privileges (maybe also reputation) instead of rep-ability)
- Bring Back the 200 rep level to not see Sponsored Header Ads (replace it with privileges)
- Delete link missing (this is about 10k abilities, so use 10k-tools instead)
Do you agree with me or do you think that tag is useful (then what should it be used for)?