Razor wire is a mesh of metal strips with sharp edges, which helps to prevent passage by human beings. The shape of the barbs also characterizes razor wire.
Generally accepted barb definition:
1. short barb razor wire has barbs from 10 mm to 15 mm long
2. medium barb razor wire has barbs 20 mm to 25 mm long
3. long barb razor wire has barbs from 60 to 66 mm long.
Although there is little research to indicate whether longer barbs are actually more effective in resisting penetration, they certainly provide a stronger psycholigical deterent.
Razor wire barbs are sharper than the barbs of barbed wire. The term "razor wire" is a slang term derived from a manufacturer's brand name. It is not actually razor sharp, but the sharp edges of the wire can cause serious cuts in any person attempting to pass through quickly.
In high security applications, razor wire can be used to supplement barbed wire, which could be circumvented relatively quickly by humans without tools. Getting past razor wire without tools is considerably slower, giving security forces much more time in which to respond.