Wall Running is a movement mechanic in Call of Duty: Black Ops III and Call of Duty: Infinite Warfare. Most flat walls can be run upon. To activate wall running, the player simply jumps towards a runnable surface and they will automatically begin wall running.
There are no weapon restrictions while wall running, and the player may continue to aim and shoot. However, turning too far from the direction they are moving in will cause them to stop running. After a short time wall running, the player will begin to slide downwards and must jump back on the wall to continue running.
In Black Ops III, the in-universe explanation for wall-running is that limb optimisation and micro-thrusters allow an augmented person to run along walls. Another explanation for this ability in exoskeletons is that advanced meta-materials are built into the exo's suits and gloves and that applying certain voltages to them allows one to control the grip applied to touched surfaces. These meta-materials exploit van der Waals forces to allow a person to gain sufficient traction to run on walls. This second explanation is also mentioned by the announcer during the tutorial for Free Run.