How to rationalise the IUPAC name for tetrahedrane?
Let's start with bicyclobutane:



The proper name for this compound is bicyclo[1.1.0]butane. The compound is numbered starting at one bridgehead and working around. The numbers in brackets represent the number of atoms between the bridgeheads. 

Now, tetrahedrane, which has an extra bridge between carbon atoms 2 and 4:



Once again, we list all of the bridges in the brackets, but we have an extra bridge, and it is not between the main bridgeheads (1 and 3). We list this extra bridgehead last and then use superscript locants to indicate which ring atoms this bridge connects. This extra bridge is between carbon atoms 2 and 4, thus $0^{2,4}$: tricyclo[1.1.0.0$^{2,4}$]butane.

For more examples, including applying the rules to crazier ring systems, here is the IUPAC publication