In the case of oral stops, the airflow is blocked completely, causing pressure to build up. The obstruction in the mouth is then suddenly opened; the released airflow produces a sudden impulse in pressure causing an audible sound.
The oral cavity can also be completely obstructed while allowing air to escape through the nose; this may be called a nasal stop. Usually the term "stop" is used to refer to oral stops only, with nasal stops called simply nasalss. Since nasals are always continuous, not abrupt, it seems strange to call them stops, though strictly the definition of stops given above allows it.
Here are some of the oral stops. (The figures in square brackets are from the IPA.)
[p], [t], [k] (voiceless)
[b], [d], [g] (voiced)
[m], [n], [ŋ] (nasal)
[ʔ] (glottal stop, though not as a phoneme in most dialects)
All languages in the world have stops. Some Polynesian languages have only three. Swiss German has [p, t, k, pp, tt, kk]. Most languages have at least [p], [t], and [k], and usually more.
Stops may be made with more than one airstream mechanism. The normal mechanism is pulmonic, that is with air flowing outward from the lungs. A pulmonic stop is called a plosive. All languages have plosives. Some languages have stops made with other mechanisms too: these are called ejective, implosive, or click dependent on the mechanism.
See phonetics, fricative, affricate, nasal consonant, approximant, click, phonation, airstream mechanism