Acronym for Digital Multi Meter. Also known as a VOM, Volt Ohm Meter. Fluke is the best known manufacturer; other brands may perform satisfactorily and be less expensive. For general stage use, I like this model, as it fits in one's pocket and costs $36.00. Meters can be found for as little as $4.99. Safety notice: When operating these meters, the user may be exposed to dangerous and deadly electrical current. Prior to using, read all instructions and cautions. Do not use without proper supervision and training. It is strongly suggested that any meter for stage use be CAT II-rated or better. See http://ecmweb.com/ops/electric_need_know_category/ for an explanation of category ratings. For rudimentary instructions on some common uses, see http://www.familyhandyman.com/DIY-P...al-Tools/how-to-use-a-multimeter/Step-By-Step.