Paralanguage refers to the non-verbal elements of communication used to modify meaning and convey emotion. Paralanguage may be expressed consciously or unconsciously, and it includes the pitch, volume, and, in some cases, intonation of speech. Sometimes the definition is restricted to vocally-produced sounds. The study of paralanguage is known as paralinguistics.

The term ’’paralanguage’’ is sometimes used as a cover term for body language, which is not necessarily tied to speech, and paralinguistic phenomena in speech. The latter are phenomena that can be observed in speech (Saussure's parole) but that do not belong to the arbitrary conventional code of language (Saussure's langue).

The paralinguistic properties of speech play an important role in human speech communication. There are no utterances or speech signals that lack paralinguistic properties, since speech requires the presence of a voice that can be modulated. This voice must have some properties, and all the properties of a voice as such are paralinguistic. However, the distinction linguistic vs. paralinguistic applies not only to speech but to writing and sign language as well, and it is not bound to any sensory modality. Even vocal language has some paralinguistic as well as linguistic properties that can be seen (lip reading, McGurk effect), and even felt, e.g. by the Tadoma method.

One can distinguish the following aspects of speech signals and perceived utterances:

Perspectival aspects: Speech signals that arrive at a listener’s ears have acoustic properties that may allow listeners to localize the speaker (distance, direction). Sound localization functions in a similar way also for non-speech sounds. The perspectival aspects of lip reading are more obvious and have more drastic effects when head turning is involved.

Organic aspects: The speech organs of different speakers differ in size. As children grow up, their organs of speech become larger and there are differences between male and female adults. The differences concern not only size, but also proportions. They affect the pitch of the voice and to a substantial extent also the formant frequencies, which characterize the different speech sounds. The organic quality of speech has a communicative function in a restricted sense, since it is merely informative about the speaker. It will be expressed independently of the speaker’s intention.

Expressive aspects: The properties of the voice and the way of speaking are affected by emotions and attitudes. Typically, attitudes are expressed intentionally and emotions without intention, but attempts to fake or to hide emotions are not unusual. Expressive variation is central to paralanguage. It affects loudness, speaking rate, pitch, pitch range and, to some extent, also the formant frequencies.

Linguistic aspects: These aspects are the main concern of linguists. Ordinary phonetic transcriptions of utterances reflect only the linguistically informative quality. The problem of how listeners factor out the linguistically informative quality from speech signals is a topic of current research.

Some of the linguistic features of speech, in particular of its prosody, are paralinguistic or pre-linguistic in origin. A most fundamental and widespread phenomenon of this kind is known as the "frequency code" (Ohala, 1984). This code works even in communication across species. It has its origin in the fact that the acoustic frequencies in the voice of small vocalizers are high while they are low in the voice of large vocalizers. This gives rise to secondary meanings such as 'harmless', 'submissive', 'unassertive', which are naturally associated with smallness, while meanings such as 'dangerous', 'dominant', and 'assertive' are associated with largeness. In most languages, the frequency code also serves the purpose of distinguishing questions from statements. It is universally reflected in expressive variation, and it is reasonable to assume that it has phylogenetically given rise to the sexual dimorphism that lies behind the large difference in pitch between average female and male adults. In text-only communication such as email, chatrooms and instant messaging, paralinguistic elements can be displayed by emoticons, font and color choices, capitalization and the use of non-alphabetic or abstract characters. Nonetheless, paralanguage in written communication is limited in comparison with face-to-face conversation, sometimes leading to misunderstandings.