busy signal

noun

1. Telephony.,  a regular succession of buzzing tones transmitted to a caller to indicate that the circuit serving the number is blocked or in use, rapid repetition indicating that the network is blocked and normal repetition that the telephone being called is in use.

busy signal

noun

1. Also called (especially in Britain): engaged tone. a repeated single note heard on a telephone when the number called is already in use

Word History and Origins

Origin of busy signal¹

First recorded in 1890–95