A multimeter is an electronic instrument that allows you to measure many basic electrical quantities. The basic ones usually measure:

Voltage and resistance are measured in parallel, while current is measured in series. This is because voltage is a relative drop between two points; it is usually assumed that if someone says that something is '500 Volts', then it is 500 Volts relative to ground. It is quite possible for there to be only 3 volts difference between two points on a circuit and megaVolts between either of those points and you.

Multimeters often do other things, such as measure battery voltage under load, measure capacitance, check transistors and diodes, and even measure frequency sometimes.

Advantages of Analog Multimeters over Digital Multimeters

  • If a circuit has a changing voltage, you can see that fact easily, and sometimes even get an idea how it is changing without resorting to an oscilloscope.
  • Similarly, in a digital circuit you can produce an instant average value. This is particularly useful if you toggle an output bit between busy and not-busy -- hook up an analog meter and you can instantly discern the idle status of the system.
  • Often cheaper.

Advantages of Digital Multimeters over Analog Multimeters

  • Easy to read.
  • Has the capability to be touch hold -- which allows you to stick your probes into a dangerous circuit and pull them out before reading the value.
  • Has the capability to be autoranging.