As long as you document your research in the question, you'll probably be OK. Let me illustrate with an example.
If it's OK, I'll use your question What's the definition of "Splashware"?
If I Type:
"splashware" (ceramic,pottery)
into Google, and browse the first page of the results, I can see that:
- Splashware is "a technique for decorating pottery vessels using different colours beneath or on a lead glaze. During the firing process the colours spread irregularly, as if splashed on the body".
- It normally earthenware "splashed with polychrome glazes".
- The splashware technique with polychrome glaze was derived from Chinese T'ang pottery.
- From China the technique spread to the Islamic and Byzantine worlds, with examples found from Afghanistan and Iran in the east to Turkey and Cyprus in the west.
If that is all you need, then the question is "a request for trivia", as they say round here, and so is going to be off-topic. If you want more than that, the you should include all of the above in your question and explain why it isn't a sufficient answer.
Another way to think about it is that the bar to be cleared here should be Mark's "preliminary research test".
It can also be helpful here if you familiarise yourself with some useful Google search techniques.
For your example questions
I suspect that the first question might just be on-topic here. While it is trivial for me to answer, it might not be for someone who doesn't know to search for "fibula" in the context of a brooch.
I think the second might be considered off-topic, but then we are back to the question of do people know what a "fibula" is in this context.
I would certainly argue that the third question was on-topic. The specific use of the terms in archaeology - and by extension in historical articles and journals - differs from common modern usage. Provided that it made explicit reference to an historical or archaeological context (e.g. the UK Portable Antiquities Scheme), I think that this would be on-topic here.
To clarify my answer to the third question above (since the comments below seem to indicate some confusion) consider the example of an escutcheon plate on a lock:
The function of an escutcheon plate is obvious - it protects the wood around a keyhole from damage when keys are repeatedly entered and removed from the keyhole. They are particularly associated with warded locks and examples have been found in contexts from Ancient Rome and Ancient China. In its simplest form it is just a disk or rectangle of metal with a hole of appropriate size and shape cut into it. Most of us would consider this to be a "furniture fitting".
But I suspect that most of us have also seen much more elaborate escutcheon plates, for example:
]
This still performs the function of an escutcheon plate, but is also now a decorative item. Is it now a "furniture fitting", or a "furniture mount"? Where should we draw the line?
There is no hard-and-fast rule.
These are just labels used by archaeologists to describe groups of artefacts. Hopefully all the archaeologists working for a particular unit will be consistent (if that unit actually has guidance that specific!). Failing that, we might hope that each archaeologist would use the terms consistently. When we start talking about archaeologists working in different countries, all bets are off ...!
Modern furniture makers are somewhat indiscriminate in their use of the terms (which, I suspect, was the root of the problem when you asked that question on DIY:SE).
