Gas consumption refers to your real-time consumption rate of gas during a dive. In other words, it is the amount of gas a diver would use in one minute on the surface. This is commonly known as your surface air consumption or SAC rate.
Gas consumption rate is measured in liters per minute (cubic feet per minute). This is an optional field and needs to be added to your custom dive mode views in DM5. In the classic view below, gas consumption rate is in the bottom right corner.
For enabling gas consumption metering, see How to enable gas consumption metering.