So I just sorted out a list of almost every tail tags for myself.
Here are my questions:

1. Rename tail_coil to tail_coiling?

just popped out recently (while I am editing wiki) for distinguish between coiling.

My thoughts:
I think this tag can stay. But I would like it to be renamed to tail_coiling, to keep it consistent with coiling. I am not sure if it should also implies coiling.

2. Is coiled_tail still needed for tagging?

I see there is a lot problems between this and tail_wraps. Then I just noticed that these tags can cover that part pretty well:
tail_around_leg / tail_around_waist / tail_scarf / entwined_tails

They are more intuitive than coiled_tail / tail_curl / wrapped_tail or whatever I cleaned up, I think. If there is anything not covered, that would be just tail_around_arm and tail_around_object.

Example:
post #160626 post #854970

By the way, I think many of them should not be tagged prehensile_tail, because their tail are not trying to grab something around, or coil on something to balancing themself.

• See also: forum #97285 - \tail_wrap usage (Jan. 2014)
• See also: forum #151535 - Wraps (Feb. 2015)

3. The tag for bandage-like tail_wraps

Example:
post #386804

My thoughts:
Use tail_bandage instead. Correct me if bandage and wraps are not same, because I actually don't know the differences. I always call that bandage.

• See also: forum #188816 - Something needs to be DONE about tail_wrap (Mar. 2016)

4. hanging_by_tail and lifted_by_tail

They are messed up, we need a clear definition on wiki for them.

My definitions:
hanging_by_tail is using the tail's own force to suspend in the air. Commonly with prehensile_tail.
lifted_by_tail is to be suspended in the air by external force.

5. Usage of tail_play?

The range is ambiguous, so I want to suggest mine. I think tail_play should be used only when:

• The tail is rubbing the genitals, not penetration / tailjob / tail_suck / tail_lick.
• The tail is grabbed by hand and used as sex_toy.
• Stroking the tail like a penis or other weird actions.

Example:
post #834113 post #889310 post #187509

post #470376 <- This one I would tag head_tail + tail_around_leg + tail_play, no tail_sex.

• See also: forum #156628 - Tribadism, Frottage, Tail_Sex and Penetration tag issues (Apr. 2015)
• For reference: See the description of tailplay (That tag should be aliased)

6. tail_slap / tail_swipe / tail_whip

They are same kind of movements. I would like to know if there is a word that can cover them all? But they are all underused and may not so important anyway...

7. Why is tail_mouth a species tag?

Isn't this some kind of mistake? Or because they are so cute, so the tag's type doesn't matter? I mean, @Genjar already separated some specific species to tailmouth_(species). That's good job.

• See also: forum #192713 - miscategorized tag: Tail_mouth (May. 2016)

8. What are docked_tail and bobtail?

I am unfamiliar with this subject, so I need someone to write descriptions for their wiki. That will help a lot for tagging.

9. How to tag this tail?

post #77685
Should this membranous part at the end of tail be called
webbed_tail / tail_fan / tail_fin / tail_frill / tail_membrane or what?
I want to have a tag for them. I think tail_frill is the primary choice.

10. ridges / tail_ridge / ridged_tail and spines / tail_spines etc.

Pending.
I will talk about this subject in another topic. Because they are kind of complex, and probably never discussed before.

Notes:

If someone decides to clean mistagged tail_wraps tags, please don't forget to delete wraps too.

After this discussion is settled (I hope), I would like to start updating wiki and retagging these tail tags. Just let you know, I already cleaned up some inferior or misspelled tail tags. And some of the tags that still needed to be aliased or cleaned are listed on the tail wiki.

5. tail_play...

tail_suck and tail_lick are foreplay(tail_play), other then that i agree completely, basically if its sexually stimulative but does not involve direct stimulation for the propose of orgasm or/and penetration of genitalia.

6. tail_slap...

slap would be preferable, swipe would be the formal name thru it does not always mean a impact by the flat surface of the hand palm or tail but also the act of moving a set of sharp tips(ex. claws, tail tips) across a surface to cause damage, tail_whip would seem a object rather then a action done by the tail.

8. docked_tail...

In regards to docked and bobbed there is some overlap in meaning but generally the former is were the tail has been artificially cut while the latter is a natural trait of the animal species. For tagging proposes docking would cover post showing the tail being cut(process or cut off tail part shown) or dialog giving the impression of such while bobtail covers instances of a bobbed tail shown but no process or anything thru such cases would be covered under short_tail.

https://en.wikipedia.org/wiki/Natural_bobtail
https://en.wikipedia.org/wiki/Docking_(animal)

9. untagged forms...

For both it propose and the general definition of frill, that tail would be tagged as a tail_fin. that at least my opinion. what would actualy be tagged as frill is ether a extendable sheet of skin around the neck supported by bones/cartilage or singular paths of spines or spikes that have webbing between them.