In articulatory phonetics, a consonant is a sound in spoken language that is characterized by a closure or stricture of the vocal tract sufficient to cause audible turbulence. The word consonant comes from Latin and means "sounding with" or "sounding together," the idea being that consonants don't sound on their own, but occur only with a nearby vowel, which is the case in Latin. This conception of consonants, however, does not reflect the modern linguistic understanding which defines consonants in terms of vocal tract constriction.
Since the number of consonants in the world's languages is much greater than the number of consonant letters in any one alphabet, linguists have devised systems such as the International Phonetic Alphabet (IPA) to assign a unique symbol to each possible consonant. In fact, the Latin alphabet, which is used to write English, has fewer consonant letters than English has consonant sounds, so some letters represent more than one consonant, and digraphs like "sh" and "th" are used to represent some sounds. Many speakers aren't even aware that the "th" sound in "this" is a different sound from the "th" sound in "thing" (in the IPA they're [ð] and [θ], respectively).
Each consonant can be distinguished by several features:
All English consonants can be classified by a combination of these features, such as "voiceless alveolar stop consonant" [t]. In this case the airstream mechanism is omitted.
Some pairs of consonants like p::b, t::d are sometimes called fortis and lenis, but this is a phonological rather than phonetic distinction.

The manner of articulation is the method that the consonant is articulated, such as nasal (through the nose), stop (complete obstruction of air), or approximant (vowel like).
The place of articulation is where in the vocal tract the obstruction of the consonant occurs, and which speech organs are involved. Places include bilabial (both lips), alveolar (tongue against the gum ridge), and velar (tongue against soft palate). Additionally, there may be a simultaneous narrowing at another place of articulation, such as palatalisation or pharyngealisation.
The phonation of a consonant is how the vocal cords vibrate during the articulation. When the vocal cords vibrate fully, the consonant is called voiced; when they do not vibrate at all, it's voiceless.
The voice onset time (VOT) indicates the timing of the phonation. Aspiration is a feature of VOT.
The airstream mechanism is how the air moving through the vocal tract is powered. Most languages have exclusively pulmonic egressive consonants, which use the lungs and diaphragm, but ejectives, clicks, and implosives use different mechanisms.
The length is how long the obstruction of a consonant lasts. This feature is borderline distinctive in English, as in "wholly" [hoʊlli] vs. "holy" [hoʊli], but cases are limited to morpheme boundaries. Unrelated roots are differentiated in various languages such as Italian, Japanese and Finnish, with two length levels, "single" and "geminate". Estonian and some Sami languages have three phonemic lengths: short, geminate, and long geminate, although the distinction between the geminate and overlong geminate includes suprasegmental features.
The articulatory force is how much muscular energy is involved. This has been proposed many times, but no distinction relying exclusively on force has ever been demonstrated. Consonant as a symbol

Articulatory phonetics
Table of consonants
List of consonants
List of phonetics topics