1. Vocal-auditory channel -- This means that the standard human language occurs as a vocal (making sounds with the mouth) type of communication which is perceived by hearing it. There are obvious exceptions: writing and sign language are examples of communication in the manual-visual channel. However, the vast majority of human languages occur in the vocal-auditory channel as their basic mode of expression. Writing is a secondary, and somewhat marginal form of language, while sign languages are in limited use, mostly among deaf people who are limited in their ability to use the auditory part of the vocal-auditory channel.
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2. Broadcast transmission and directional reception -- This means that the human language signal is sent out in all directions, while it is perceived in a limited direction. For spoken language, the sound perpetuates as a waveform that expands from the point of origin (the mouth) in all directions. This is why a person can stand in the middle of a room and be heard by everyone (assuming they are speaking loudly enough). However, the listener hears the sound as coming from a particular direction and is notably better at hearing sounds that are coming from in front of the them than from behind them.
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3. Rapid fading (transitoriness) -- This means that the human language signal does not persist over time. Speech waveforms fade rapidly and cannot be heard after they fade. This is why it is not possible to simply say "hello" and have someone hear it hours later. Writing and audio-recordings can be used to record human language so that it can be recreated at a later time, either by reading the written form, or by playing the audio-record.
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4. Interchangeability -- This means that the speaker can both receive and broadcast the same signal. This is distinctive from some animal communications such as that of the sticklefish. The sticklefish make auditory signals based on gender (basically, the males say "I'm a boy" and the females say "I'm a girl"). However, male fish cannot say "I'm a girl," although they can perceive it. Thus, sticklefish signals are not interchangeable.