Insta-Lust/Slow Burn – how do you define it?

These are both terms that come up a lot on here (mostly in terms of people asking for recs that do/don't include it), but unlike insta-love, it seems like everyone has a slightly different definition.

To me, insta-lust is something I mostly see in erotica, where the characters embark on a physical relationship within the first 10-20% of the book. However, I often see people use it to describe characters being immediately attracted to each other (even if they don't particularly like each other), even if it's only in their inner monologue. To me, that's as integral a part of romance as a HEA, and I feel like books that don't feature it at all are outliers.

Slow-burn seems like it has even more variation in opinions. Though I haven't read any of her books, I know Mariana Zapata is considered the queen of slow-burn, writing 500+ page doorstoppers where they don't admit their feelings until the 90% mark. Personally, I'm satisfied to call something slow-burn if the characters take at least 50% of the book to get together (physically or emotionally). Any more than that and I start to lose interest, unless the author does an amazing job building the tension.

I'm curious to hear everyone's thoughts!