Does it describe the contents of the questions to which it is applied? and is it unambiguous?
No, this tag can refer to users attempting to (a) purchase Ubuntu itself (c) buy software on Ubuntu (c) use/package commercial (purchased/purchasable) software on Ubuntu.
Is the concept described even on-topic for the site?
Yes (assuming it complies with the rest of our scope). But... this still isn't a good tag.
Does the tag add any meaningful information to the post?
Does it mean the same thing in all common contexts?
No, see #1.
Therefore, I propose that we burninate the purchase tag.
Thoughts? Anyone have a reason to keep it around?