A sequence of states representing an encoded message in a communication channel. Any variation of a quantity or change in an entity over time that conveys information upon detection. A sign made to give notice of some occurrence, command, or danger, or to indicate the start of a concerted action. An on-off light, semaphore, or other device used to give an indication to another person. (of a radio, TV, telephone, internet, etc.) An electromagnetic action, normally a voltage that is a function of time, that conveys the information of the radio or TV program or of communication with another party. An action, change or process done to convey information and thus reduce uncertainty. A token; an indication; a foreshadowing; a sign. Useful information, as opposed to noise. (computing, Unix) A simple interprocess communication used to notify a process or thread of an occurrence. (biochemistry) A signalling interaction between cells. (transitive, intransitive) To indicate; to convey or communicate by a signal. (transitive) To communicate with (a person or system) by a signal. Standing above others in rank, importance, or achievement.