noun

• (electricity) A period of low alternating current line voltage, causing a reduction in illumination.
  "When demand for electricity exceeds the available supply, a brownout occurs."
• (firefighting) A temporary closing of a fire station, usually due to budget restrictions.
  "Fire departments across the country have been forced to rely on rolling brownouts because of the recession."
• (figurative, uncommon) A moment or period where something is weakened, diminished or less effective.
• (Philippines, Australia, Hong Kong) A blackout, regardless of time of day.
  "Remember that you can't send or receive a fax if there is a brownout. ... Due to blackouts (the Philippine term is brownout), especially during the dry season, be prepared with a flashlight and don't forget to save your data in your PC."