"12V cons" is a 12v power line that is always live (regardless of whether or not the car is on). (this wire is usually yellow in aftermarket audio components*)
"12v ACC" is a 12v accessory line that is only live when the key is on the "ACC" or "ON" position. (this wire is usually red in aftermarket audio components*)
*=those are common wire colors for aftermarket car audio components and other accessories, but there is no guarantee that your GPS unit uses this wire color standard. you should check the GPS unit's manual before connecting any wires.