Speedrun

Speed running is an attempt to finish any Campaign level as fast as possible. Common methods include explosive jumping, only killing enemies if you have to, and careful choosing of weapons (ammunition count, the right job, etc.)

Speed running can also include going to certain areas to avoid enemies, or skip parts of the level, this can be seen on Halo 2, on the level Outskirts, where you can skip from the start of the level to the part where you meet up with Marines. Such tactics are very helpful on Legendary.

On the Silent Cartographer,
 * You can disable the security system without first going underground where the door locks.
 * If you have full overshields, you can jump down to the bottom of the level with the map room after the cut scene with Master Chief kicking the rock into the pit.
 * By positioning your Warthog precisely near the locked door, you can skip the security substation completely.
 * From the third level of the substation (if the first level is at the entrance), it is possible to drop onto the overshield without taking any fall damage.

Speed running is often used in campaign scoring to get the speed multiplier.