500k is bigger in value than 250k and 250k is smaller in value than 500k
pot is potentiometer in short and actual term would be variable resistor
resister is measured in ohm. 250k, 500k is what we would call, for convenience. The correct term wud be 250kilo ohm/500kilo ohm, which is equal to 250000 ohm/500000 ohm
the jump/static thingy can be due to
1) different volume level between the different pickups- more obvious if switching between humbucker and single coil
2) the contact of the selector switch- the action of selecting the selector switch, will disable one contact first, before touchnig the next contact. When we play with the selector switch, there will be a short interval where theres no contact for the selector switch for whichever pickup we wanna switch in, there will be a slight "thud" sound heard when contact is made for the next pickup(more obvious if turning up the volume). This one prolly have to see if the selector switch contact is "make before break" or "break before make" type. If wanna see more, just google for either "make before break" or "break before make"
3) Dust particle build up inside, blocking the contact on the selector switch