"Backwards Long Jump". Referred to the glitch in Super Mario 64, where if you repeatedly long jump backwards up a slope / set of stairs, you will accelerate extremely fast—so fast that you break through walls, including invisible ones.

One of the most awesome glitches in the game.
Guy 1: Did you see that 0-star TAS that SwordlessLink and AKA made?

Guy 2: Yeah, the most awesome use of BLJ I've ever seen.
by XFi6 June 21, 2008
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It is a slang term used by everyone around the world to describe blowjob, because what else would that mean?
Peach gave me a good BLJ yesterday
That girl peach really knows how to give a BLJ
by Pancakes696969 August 23, 2020
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Short for backwards long jump, one of the most famous speedrunning techniques used in Super Mario 64, and is most famously used on the Looping Steps.

Explaining:
The final star door requires 70 Stars, but you can actually enter the door early. If you try to walk up the stairs without 70 stars, you will keep walking forever. Well, unless you turn back, in which you are right by the bottom. Because the devs forgot to cap backwards acceleration, you can repeatedly blj until you start accelerating so fast you end up at the final boss room.
Just watch a video, okay? I'm not a speedrunner.
Have you seen that guy blj up the stairs? It's so ridiculous.
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