Matt, trapping is the process of cutting the sides of the limb at an angle so either the back is narrower than the belly or the belly is narrower than the back. If you cut through the limb and looked at it from the end it is in a trapezoid shape, hence the term trapped. It is helpful when you have wood which is much better at tension than compression, or vice versa. It's also helpful when you laminate with 2 woods of unequal strengths and need to keep one from overpowering the other.
Lee, I agree with Ken. Slabs are normally the pieces cut off a round log at the sawmill to square it off prior to cutting dimensional lumber. Depending on the tree, there can be lots of good wood or not so much. There's usually some slope to the slab (the top end of the tree being smaller diameter than the bottom) as well. Hopefully you can pick through what they have and get some good stuff. When I'm working wood like that I lay the cut side on the bandsaw table and snap a chalkline where the wood that's deep enough starts. After you cut on that line you can use a rip fence and rip rift sawn boards until the center cut which will be quartersawn. Also, hardwood slabs make good hide fleshing boards since they have a nice curve to them. You probably already know all this.
My only bow contribution to this thread is this 52" osage molly. It draws 55#@26" but I think it has more draw length left. It has some set, some of which was present in the stave. I heat bent it out and it came right back so I left it. It is about 3/16" thick and an inch and an eighth wide over the working part of the bow.
I've toyed with bending some recurve into the levers to see if I could get a little more draw length out of her. Given that we're experimenting I think I'll do that. The other thing I could do is continue taking off thickness until I get to full draw or the bow fails. It does have one good knot in the working limb. I expect it to give up at that spot.
George