If you've been around the Toyota 4x4 scene on the internet long enough, you've no doubt come across the term 'full floater rear axle'.
A full floater axle simply means that the axle is fully floating inside the axle tube. Normally, and specifically in a Toyota rear axle, the axle shaft has the hub attached to it, and the axle rides on the bearing at the end of the axle tube. The axle shaft has to support the weight of the vehicle, as well as transmit the torsional load out to the wheel.
In a full floating axle, like the Toyota front solid axles, the axle JUST turns the wheel, and the wheel itself supports the load of the vehicle. This makes for a stronger assembly as the axle shaft only needs to transmit torque, not bear weight too.
For more information on full floater and semi floater axles, have a read here:
Front Range Off Road (and apparently others, although I was unable to find any info on them) sells a kit that converts the rear axle from semi-floating to full-floating.
Here is an install writeup of the Front Range Off Road kit by 4Wheel Offroad: