What do you consider slow-burn?

I’ve been thinking about this a lot lately when trying to figure out what exactly slow-burn means for different books.

Is it when there is a very slow romantic build-up? A slow sexual build-up? A combination of the two? I usually don’t mind a slow-burn novel with a lot of pining before they come together, but some books labeled slow-burn are also slow to develop feelings / attraction at all.

I’m just curious what other people think (or if there’s a definite answer and I’m just unaware!)

And for the slow-burn lovers, is there a favorite type for you? Or one you don’t like?