Paul, it seems that you might benefit from reading up on mandolin and picking up a beginner book on self-teaching the mandolin. The chop is a staple of bluegrass playing. If you listen to the mandolin in almost any bluegrass song, when it isn't playing a solo (lead break) it is playing a fast, staccato chord on beats 2 and 4. This is the chop. The "G chop" is such a chord formed at one of the main fretboard positions, and the so-called G-chop is movable. If you finger the mandolin thusly: 7-5-2-3, this is the G chop, because it is a G chord. If you move it over toward the top of the mando one string and leave out the E string, it is the C chop. Move the C chop up two frets and it is the D chop. Add the second fret on the highest (E) string to the D chop and you have the 4 finger D chop. By moving these three chop chords around, you can play 75% of bluegrass tunes, maybe more. There's a lot more, but I'll stop here for now.
"I thought I knew a lot about music. Then you start digging and the deeper you go, the more there is."~John Mellencamp
"Theory only seems like rocket science when you don't know it. Once you understand it, it's more like plumbing!"~John McGann
"IT'S T-R-E-M-O-L-O, dangit!!"~Me