Abbreviation for "Battery Elimination Circuit". Receivers that feature BEC (most do) do not require a separate battery pack to power itself and the servo. It draws the power from the battery pack that is powering your ESC and motor. This should not be confused with nitro cars and trucks, which do require a separate battery to power the receiver and servos. This is because with a nitro car, there is no ESC, and thus there is no battery pack to supply power.