What is a multimeter? What is the difference between a multimeter, a voltmeter, an ammeter, and an ohmmeter?

What is a multimeter?  A multimeter is an tool that is capable of measuring two or more electrical values.  Most all will be capable of measuring voltage, amperage, and ohms.  Earlier meters were only capable of measuring one type of electrical value, so a person would have to carry a meter for each unit they needed to measure.  Later meters were designed with a rotary switch so they could measure multiple units of value, hence the term multimeter.

What is the difference between a multimeter, a voltmeter, an ammeter, and an ohmmeter?  In modern times, these terms are used interchangeably and all refer to a multimeter.  Volt meters measure voltage, amp meters measure amps, ohm meters measure ohms, and multi meters measure a combination of two or more of these.