A brown out was a condition in which all electrical components were supplied with a minimal amount of power for operation. Such a failure could be due to power generation facilities being damaged or nearly depleted.
In 2364, L.Q. Clemonds, analyzing his situation after emerging from cryostasis, said, "The whacko who sold me this scam said that by putting us in orbit there would be no chance of brown out." (TNG: "The Neutral Zone")