What does "slow burn" mean?

In the last posted chapter of DD's MDZS WIP, the main characters (spoiler!) finally kiss! After more than 100k, but less than a month actually passed in the story. So we talked about the term "slow burn" and decided that similar to game speedrunning categories, there should be categories for "slow burn."

Poll #25610 Slow burn

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Open to: Registered Users, detailed results viewable to: All, participants: 55

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"Slow burn" means the relationship develops slowly from the point of view...

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of the characters
2 (3.6%)

of the reader
5 (9.1%)

both
12 (21.8%)

either/or
3 (5.5%)

mostly the characters, but not too fast for the reader either
3 (5.5%)

mostly the reader, but not too fast for the characters either
27 (49.1%)

idk it's just a gut feeling
3 (5.5%)

other (please comment)
0 (0.0%)