4-terminal shunt resistor
Take a look at this. It shows two terminals as the main current flow (thick tracks) and uses 2 more terminals for measurement of the volt drop generated by that current: -



The "better" way is on the left because it takes measurement connections from a defined place and at no point on those measurement connections is there load current flowing.

The picture on the right shows the measurement connections at some small distance from the shunt resistor terminals and therefore there is a small volt drop that forms an error - in effect you can't rely on the stated value of the shunt resistor in order to convert the measured voltage to an assumed current flow.