I wasn't allowed to add the "Windows 10" tag to my question, which was specific to Windows 10. What is the purpose of prohibiting people from asking questions specific to Windows 10?
4Which site were you on? You should probably ask on that site's meta.– TRiGDec 19, 2017 at 15:24
3@TRiGisTimothyRichardGreen: OP does not have enough rep on their other site(s) to ask questions on meta except in regard to a specific question, which is not really ideal. In any case, the general explanation has already been given and is topical here.– Nathan TuggyDec 19, 2017 at 19:22
The reputation requirement doesn't prevent you from asking a question about Windows 10; rather, it prevents you from creating a tag windows-10. This is to avoid multiple 'wrong' tags being created; it takes a while for a new user to get the concept of tags (even experienced users get it wrong regularly); therefore, it requires 300 reputation to create a tag (on a beta site, it's 150 reputation). Because of past waves of tag creation 'abuse', it requires even more reputation on Mathematics Stack Exchange (1000) and Stack Overflow (1500); see Reputation requirements compared.
1What is the purpose of tags? I though it was to allow people to locate questions about specific hardware, software, etc.so that they can answer them. How is the "Windows 10" tag any more prone to abuse than the "wake-on-lan" tag that I am graciously permitted to use? Dec 20, 2017 at 8:08
4The 'abuse' I'm referring to is mostly about the so-called meta tags, but also misspellings ([windos-10]) and different versions of the same tag ([windows10] vs. [windows-10]). Dec 20, 2017 at 8:11
I think I see now. I thought I selected the "Windows-10" tag but maybe I typed "Windows 10". Perhaps it would be more clear if the response to the latter were a list of similar tags to choose from. Presumably, if I had a high enough reputation, a new tag would have been erroneously created. Dec 20, 2017 at 9:26
1Yep, that would've created two tags [windows] (which already exists) and  (which does not exist, for good reasons). Dec 20, 2017 at 9:27
Here on Super User, you only need 300 reputation to create tags. Jan 4, 2018 at 21:27
@DonaldDuck yeah, that information was correct when the question was originally posted on Meta Stack Exchange. I've updated my answer, thanks. Jan 4, 2018 at 21:46
You need a minimum reputation to create a tag. On say, Super User, where windows 10 is on topic there's a preexisting tag. you can already use windows-10. On other sites, there may be less of a reason to.
Since tags are often created without a real need (and it's a little too easy to make a bogus tag), the minimum reputation level needed to create them is a nice way to ensure people who create new tags know how things work (and to keep spammers from abusing it, 'cause they're why we can't have nice things).
Assuming you were trying to ask the question on Stack Overflow, you had multiple existing tags to choose from:
No need for a new tag.
If you need to ask a Windows 10 question on a site that doesn't have that tag, you should first make sure your question is on-topic on that site. If it is, you can still ask it, but without the Windows 10 tag.