I know that there was a question asked very early on in this sites life about the animal name tags:
Should our pet tags be plural or singular?
The general consensus there is that animal pet names should be plural, i.e. dogs, cats, frogs.
However, in a couple of recent meta answers (here and here), I've seen people interpret this to mean that all tags on pets.SE should be plural.
Is this what we really want?
I understand that we have decided to use plural tag names for animals. However, I don't think we should have a blanket rule on all tags being plural.
Take, for example, the aquarium tag. With the current name, the tag can either be thought of as a noun (meaning the enclosure housing fish) or an adjective (as in "aquarium pets"). Both meanings are related and work well with the questions on this tag. If you make the tag plural, you don't have that anymore. Add to that the fact that there are two different valid plural forms of aquarium, and I don't see any good reason why the aquarium tag should be made plural.
There is no general "plural" rule. I have said that I think tags for counting nouns work better as plurals -- cats, dogs, treats, etc. However, mass nouns, like "medicine" or "discussion", and "effectively-mass" nouns, like "behavior",1 are different. And, of course, there can be tags that aren't nouns.
So I think we have a preference but not a rule, and even if there were a rule it wouldn't apply to everything. We can use common sense here.
1 Let's not get pedantic. Yes, "behaviors" is a counting noun referring to different, distinct behaviors. It's also a mass noun referring to the concept of behavior in general. I'm trying to communicate a concept, not get bound up in prescriptivist grammar.
