Is that a page where you ask for someone's email address?
Yes, but it's not
quite as simple as that. A page where you ask for someone's email address (so as to be able to send them email with their permission) is an "opt-in page". A "squeeze page" is a
specific type of "opt-in page". (All squeeze pages are opt-in pages, in other words, but not all opt-in pages are squeeze pages).
A "squeeze page", specifically, is a page with a box for the user to submit an email address (and/or any additional contact details required/volunteered) on which the
only other content is text (and/or occasionally video/audio, but not in this context) incentivizing the opt-in. That "only" is a big word: it's the defining characteristic of "squeeze pages".
In marketing language, strictly speaking a squeeze page also contains no other links to any other on-site/off-site pages, either. The only ways to get off a squeeze page are the "submit"/"sign-up"/"enrol"/"subscribe" button, the browser's "back" button and the little red cross that closes the window. Anything else is known in the trade as a "leak" (i.e. additional and unnecessary option which can serve only to reduce the conversion-rate).
People sometimes think of pages on blogs offering a little opt-in box in the sidebar with some text along the lines of "Subscribe here for update notifications" or whatever as "squeeze pages", but they're mistaken in doing so, and the conversion-rates of those "opt-in boxes" are typically a tiny fraction of those resulting from squeeze pages.
No; not at all. But it can be very helpful. As marketing people always say "the money is in the list". (It isn't literally true, of course: the money is really in the relationships built with the list subscribers and the extent to which they're subsequently willing to read, pay attention to and act on email communications sent out by the list-owner).
I had a business partner for a while and she was HUGE on building an email database to send offers as a marketing tool.
Not so easy to comment without knowing more about the context, but in general, emails sell
overwhelmingly more than websites do.