This happens when someone asks you about a fairly new song. You can't remember the lyrics or the music, but when it comes on the radio, you'll know that's the one. What adjective would describe that "elusive" song? I don't think "elusive" is the right word here because the song itself isn't sneaky or hard to identify or define (according to general consensus).
This works the same way when you can't remember a face, but when given a bunch of photos, you'll be able to quickly identify that
adj. I need here person you're trying to remember, if among those photos.
I would be having what I've been told a "brain fart" or a "senior moment", but what would you call that which you just can't think of at the moment? Is there also a noun form for it?