The Turbo name has been around for quite some time, but is still widely unknown. The majority of Tricktheory uses the terms and definitions in the Aeriform system to frame things, however Turbo is not a part of that system. It has been included because it is a common enough term to deserve some explanation.
In short, Turbo landings are 2 footed landings. In TKT, for the vert axis, this simply a Hyper. This tends to confuse people who think of Hyper as only landing on the kicking foot. On the invert axes, Turbo is typically used to describe kicking variations that land solidly on both feet.
Perhaps the most common use of the Turbo landing from the invert axis is in the shuriken-hyperhook. Technically, the landing stance, which is based on rotation first and foremost is a mega or semi, however most trickers think of these landings as singular or sequential landings with relative forward positions, which is where Turbo becomes very convenient.
Another somewhat common use of the Turbo tag is in vert kicks utilizing a round kick. A turbo tornado is useful for landing in backside, on both feet. It is somewhat similar to a parafuso, where the feet come together at the very end, right before landing, rather than on the target. Typically this is used for punching, or reverse-popping.