Tyre boot is a temporary solution for a tyre that is cut or badly damaged, when one doesn't have a spare one. It's a piece of material that is put between the tube and the tyre and which prevents the tube to bulge out through the cut in the tyre and explode. The boot material could be of any kind, as long as it is strong enough to hold the pressure and soft enough not to puncture the tube. It's often recommended to use a piece of the old tyre, although from my experience even a boot made with duct tape did last more then 1500 km (on tarmac).
My hint is that before putting the boot, it very much helps to sew the tyre. If the tyre casing is cut or damaged, I sew up that part with the needle and thread, just as patching a hole in a sock. Then I apply the tyre boot, which in this case can be as simple as a piece of duct tape or a tube patch, applied from the inside of the tyre. A piece of wrapping material (for chocolate bars, for example) might be just as useful.
I have such patched tyres on my commuter currently, both at front and rear, as an experiment of how long this would last. This is a road bike with a pressure of 6 bar. I've been riding 18 months now with patched front tyre and 14 months with the back one, but after I'd confessed it, and Murphy is reading it, I suppose I'll have a blowout tomorrow - will let you know.