if some google search was done, the info would present by itself...
Mfd, aka microfarad, is the unit of capacitance. Just like for length, its millimeter, centimeter, meter, kilometer etc
pico, micro etc, is the measurement to how many decimal points
the 600v, is the voltage rating of the cap. 600v is the maximum limit of the thing. Passing beyond 600v thru the cap, you will create firework out of the cap. Any voltage below 600v passing thru is within the allowable operating range of the cap.
in comparison, in geetar wiring circuit. The amount of voltage that the capcitor is "seeing", its in the range of millivolt. Theres no point to lost sleep over voltage rating in geetar circuit, its almost as good as using a 20 storey building to avoid the rain when an umbrella can do the same thing..
the voltage rating can be ignored when dealing with geetar work in general. Just need to know the value of the cap. The material and value of it are the factors that determined the slight different in sound. The rest...? Heh, mojo talk and marketing.