Bit of a minefield that on WF.

Some would say nothing...... that they are the same thing.

Others would say that frailing is the relatively simple technique of hitting a note then brushing a number of strings and then releasing the 5th string with your thumb. Count 1-2-3-4..... 1/pick 2/ nothing 3/ brush 4/ thumb release top string.

Clawhammer is a development of this where you add in drop thumbing, double thumbing (hitting top string on 2/ & 4/) , pull offs, slides and hammers to add more of the melody notes in. Chances are the 2/ beat as described above will have a note sounded and 3/ might also be a single note rather than a brush.

Some may argue with this description..... it would be far easier to show you than explain!