When an agent asks for the first five pages of text to be sent with the query, are they referring to literally the first five pages, i.e. which would include the prologue, inspirational quote, etc. Or do they want only the first five pages starting at chapter one?
They mean the first five of whatever starts the story off. If your prologue is largely unrelated to the story that follows, don't count it. If it starts the story, count it - and send it. Generally I'd say send the prologue anyway, because that's where your story (whether fiction or non-fiction) starts and the agent wants to read from the start. We usually make our decisions very quickly - after you've been an agent or commissioning editor/publisher for a while, you start to know the signs - so we usually don't even need the first five pages to tell us if we want to read more. I've sometimes requested a full manuscript after reading the first two sentences. This does not mean that you should polish your first sentence, paragraph or page to within an inch of its life. You can either write what we want to read, or you can't, and we'll know that when we see it. Also bear in mind that everyone's taste is different. I've turned down manuscripts that went on to get published but I've never regretted turning them down - they weren't for me, and if I don't love something I can't get it published.
So that answer digressed from the original subject. Accordingly, I'll give you a short recap: take the five pages from where the story starts.