A meter in an electrical circuit measures electrical what?

Depends on the kind of meter.
Voltmeter measure the volt,
Ammeter measure the amperage, the amount of electricity has been used.
Another Answer

There are lots of different type of meter, the most common being:
  • ammeter -measures current
  • voltmeter -measures potential difference
  • ohmmeter -measures resistance
  • wattmeter -measures power
  • energy meter -measures energy