It's hard to categorize a crashpad into anything other than it's a place where multiple flight crewmembers spend the night.

From there, crashpads vary to each extreme. To stay true to the term crashpad, I would define it as a place (such as an condo, townhome, or house) that is solely used by crewmembers for short term stays. The number of crewmembers might be as low as the number of bedrooms (although I really don't think of that as a crashpad), to as high as 20 or 30 people.

The cheapest crashpads usually have multiple beds set up and keep the rent cheap (100-200/month), and have short term "leases" like month to month.

The best way to find crashpads is to ask around with other crewmembers or by hunting bulletin boards around the crewroom or training center.