Difference between low impedance fuel injector and high impedance fuel injector
Put simply, the impedance allows you to work out you how much current it will take to make it open. Because an injector is a solenoid, it presents an inductive load rather than a simple resistive one, so the power consumption will be defined by the impedance, frequency of operation and the amount of time it spends open.

Low impedance injectors open and close more quickly but take more power to operate. They tend to be used for larger engines, or smaller ones with forced inductance, where the requirements for fuel flow are higher. They also tend to take a higher current to make them open but less current to hold them open, while high impedance injectors take the same current to open and hold.