(US, telephony) An audible signal to the calling party that indicates failure to complete the requested connection; an engaged tone

A transmitter encodes data by producing a signal which is a continuous stream of signalling events each which has sufficient information for the receiver to recover the original data. Just like a quantum leap is the smallest measurable leap, a signalling event is the smallest possible amount of signal that the receiver needs to recover the original data without error.

plural of traffic signal

Alternative form of time signal

plural of time-signal

plural of time signal

plural of signal box

A building, typically adjacent to or spanning a railway line, from where signals, points and (sometimes) level crossings are controlled. / The alarm-box of a police or fire-alarm system.

(biochemistry) A series of chemical reactions within a cell which start when a transmembrane protein comes into contact with a chemical signal, resulting in a second messenger being triggered.

(endocrinology) A type of cell signaling involving the release of a hormone from a nerve cell that has an effect on another cell.