Wikipedia
Dumsor pronounced "doom-sore" (or more appropriately dum sɔ, "off and on") is a popular Ghanaian term used to describe persistent, irregular and unpredictable electric power outages.
The term is derived from two separate words from the Asante Twi, the Akuapem Twi or Fante dialects of the Akan language (a language spoken widely in Ghana), dum (to turn off or quench) and sɔ (to turn on or to make light), so the term roughly translates as "off-and-on". The term has also recently evolved into "dum dum: sɔ no mma" ("off and off") due to the increase in the intensity of the power outages.
The frequent Ghanaian blackouts are caused by a power supply shortage. Ghanaian generating capacity is currently 400-600 megawatts less than Ghana needs. Ghanaian electricity distributors regularly shed load with rolling blackouts.
At the beginning of 2015, the dumsor schedule went from 24 hours with light and 12 without to 12 hours with light and 24 without. The long blackouts contrast with the practice in other countries, where blackouts roll rapidly so that no residential area is without power for more than one hour at a time.