When the voltage drops, it is called a brownout, but when the power goes off it's a blackout.  While brownouts can do more damage to equipment than blackouts, it the latter which we really fear--sitting at home in the dark.  In business or industry, however, it means your productivity has gone to zero.  When the power goes off, you light a candle and get hot under the collar, both of which never really seem to eliminate the situation.