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.
Origin of busy signal
First recorded in 1890–95
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
British Dictionary definitions for busy signal
US and Canadian a repeated single note heard on a telephone when the number called is already in useAlso called (especially in Britain): engaged tone
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012