Some of the questions are okay, and some are not. It really helps if you ask the question in a way that indicates that you've done your homework.
For example, if you just want a definition of Borel subgroup or some basic context, you might as well read the Wikipedia article, or even better, consult a standard text on algebraic groups. The same is more or less true for Picard-Vessiot extension. If you want something above and beyond such references, then your question should not have the simple "what is" form, and should be more specific.
One situation where such a question is (in my view) unambiguously reasonable is if you are asking about something that has appeared recently. In this case, there may not be standard references, and it is possible that only a few specialists have a good grasp of the mathematical context. In this case, you shouldn't be surprised if it takes a while for a good answer to appear.