Strafe jumping, along with wall running, is a bug in the quake engine that allows you to get to key areas faster or to places you normally wouldn't be able to reach. Strafe jumping is done by sprinting forward, turning to the left/right, and pressing your left/right strafe key respectively. Once you turn, you jump at a certain angle, and it propels you faster/farther. In general ProMod movement, you typically try to do a good strafe jump near the end of your sprint duration. This, combined with wall running, gives you a bit of extra speed moving around the maps. It takes a bit of time to master, but it's a great thing to know and use. Also, keep in mind that most people are better at strafing one way than the other (*generally* right-handed people are better at left-strafing, but this isn't always the case). For a more in-depth tutorial, visit CodJumper

Here's a strafe tutorial made by Tom "D1ablo" Newman

Strafe tutorial by Tom "D1ablo" Newman