I think most people use the terms "dungeon crawler" and "blobber set in a dungeon" interchangeably, except that "dungeon crawler" can also include some of those oddball "single character blobber" games like Anvil of Dawn and Vaporum.
I think it's more complex than that because the question of what constitutes a dungeon also remains open. For example, an area may be narratively a forest or a swamp, but mechanically a dungeon, like in the aformentioned Anvil of Dawn. Even a whole open world may be one big dungeon in the mechanical sense, like the example of Wizardry 7 shows.
On the other hand, Ultima Underworld or Arx Fatalis aren't blobbers but still totally dungeon crawlers. I would even go as far as to suggest that Dark Souls is one.
I'd say that the defining traits of a dungeon crawler in the most abstract sense are 1) lack of downtime and safe areas (which makes everything into a dungeon in the mechanical sense) and 2) exploration-based rather than story- or quest-based progression (which removes the need for downtime or story dispensation areas). Basically, if there's nowhere to return to from a dungeon to recuperate and get your next task, you're in a dungeon crawler, no matter what it looks like.
When I released Legends of Amberland I got surprised when basically all press started to call it "Dungeon Crawler", even though it's more like an open world and dungeons are just part of it... In addition, when I tried to find a Steam filter for Blobbers (see: "List of all Blobbers on Steam" topic) I noticed that EVERY SINGLE game that had something even remotely like a dungeon of some sort (including RPGs in space where technically there are no dungeons
) had "Dungeon Crawler" tag. Basically, this term is used extremelly broadly and in practice, well, it does not even need the "dungeon" part to be named that
So, it's used in context of some sort of dungeon-likish-but-not-necessarily-a-dungeon area which you CRAWL (the crawler part being much more important than the dungeon part). Which I suppose makes sense, if for example there was an RPG which plays like a dungeon crawler but located in a tower (let's even assume that it's a tower without windows, so the difference is that there are different textures for walls and you go up instead of down), most would not want to exclude it from dungeon crawlers.