This was a mechanic that was in the original Half Life games, it comes from GoldSrc (https://en.wikipedia.org/wiki/GoldSrc), the original Half Life engine, being a heavily modified Quake World engine. It's funny you mention Overwatch, because many of the old Quake players are now playing Overwatch competitively. In Quake this kind of movement is a part of the gameplay, but for Counter Strike, many of the maps were not designed with the intention of this kind of movement being used. The result was people were able to do things like get into the skybox. Even though you can't bunny hop in Counter Strike like you could back then, there are still movement tricks, and maps specifically made for practicing movement. At the time there was also TFC, which was more willing to sacrifice 'realism' for game play, but Team Fortress had also existed previously for Quake World as well. All of that said, right now the most played game is Fortnite, and it definitely does not put realism first.
Oh, how we worked on our quake jumping skills, trying to get from the long passage over to a hill on the other side of some water. Q2DM1: The Edge.
We also played a lot of actionquake later. We made maps especially for jumping with this technique but I can't remember ever calling it bunnyjumping.
Funny, yesterday my daughter found how to move faster in some game by pressing strafe and forward at the same time. Had some fun to explain how that works with math in programming :-)
You might of heard the term 'strafe jumping' used in place of 'bunny jumping', they are actually different things, but depending on the game you played the term might of been used interchangeably.
"The main difference between the two is that Bunny Hopping requires the player to release the forward movement key immediately upon strafing."
In other words, if you were playing Q1/Quake World, to gain speed, you would jump and only press left and right. To keep going straight you would flick your mouse in the opposite direction that you were pressing on the keyboard. Although there are a bunch of other small tricks. In Quake 3 you would be required to press forward and left/right, unless you were playing something like CPMA. You also had more air control in something like Q1/Quake World.
It is pretty interesting from a gaming and programming perspective :). Also, not about mechanics, but Q2 CTF was really fun at the time :D
