Ahop (ABH/AFH)

Ahop, short of "accelerated hopping", is a technique that involves tricking the game into giving you more speed when you jump than you are supposed to receive. In Portal, this is done by jumping while looking in the opposite direction of your movement.

One thing to note about ahop is that it is exponential. This means that the higher your speed is, the more speed you gain every jump. This is why ahop is so powerful for speedrunning.

There are multiple ways to achieve this, and they are all listed below.

ABH

ABH, or "Accelerated Back Hopping", is where you ahop by jumping backwards. You can do this in a number of ways, but the most common way is to walk forward, jump and crouch, then turn around before you hit the ground. Then from there, you start bhopping. This is the easiest way to ahop, and technically the fastest way to ahop, because other forms of ahop require counter strafing. However, since you are backwards, you can't see where you're going. For this reason, you start to see AFH used more at higher levels of play.

AFH

AFH, or "Accelerated Forward Hopping", is where you ahop by jumping forwards. This is done by walking backwards, jumping and crouching, then jumping and counter strafing as soon as you hit the ground. For every subsequent hop, you will also need to counter strafe. In a typical situation, counter strafing is just tapping +back right before you jump, and letting go of +back right after you jump.

+strafe

+strafe is an alternative to tapping a movement key to initiate an AFH. This is done by binding a key to +strafe in the console, or by binding Strafe modifier in the keyboard options. In place of tapping S for instance, you would hold your +strafe key, slowly move your mouse down and jump. This gives AFH a lower skill floor, since using +strafe will give you much lower backward speed than if you were to tap S. But due to it being a relatively unique method of control, it can take a lengthy adjustment period to apply it to many parts of the game.