5 angle valve job is just what it sounds like, the seat and valve face are cut at 5 faceted angles. The idea behind it is that this will allow the valve to "shed" air easier as it flows into the cylinder, and then have more, thinner seperate rings on the valve seat on which to seal during combustion.

In actuality, for the street, a 3 angle job is more than sufficient, and does not risk valve damage as much since a 5 angle job can weaken the valve at the edges of the head, leading to breakage.