In phonetics, an occlusive, sometimes known as a stop, is a consonant sound produced by occluding (i.e. blocking) airflow in the vocal tract, but not necessarily in the nasal tract. The duration of the block is the occlusion of the consonant. An occlusive may refer to one or more of the following, depending on the author:
Oral occlusive may mean any of the above apart from nasal occlusives, but typically means stop/plosive. Nasal occlusive may be used to distinguish the simple nasal sounds from other nasal consonants.
The terms 'stop' and 'occlusive' are used inconsistently in the literature. They may be synonyms, or they may distinguish nasality as here. However, some authors use them in the opposite sense to here, with 'stop' being the generic term (oral stop, nasal stop), and 'occlusive' being restricted to oral consonants. Ladefoged and Maddieson (1996) prefer to distinguish 'stop' from 'nasal'. They say,
All languages in the world have occlusives and most have at least the voiceless stops [p], [t], [k] and the nasals [n], and [m]. However, there are exceptions.
Colloquial Samoan lacks the coronals [t] and [n], and several North American languages, such as the northern Iroquoian languages, lack the labials [p] and [m]. In fact, the labial plosive is the least stable of the voiceless stops in the languages of the world, as the unconditioned sound change [p] → [f] (→ [h] → Ø) is quite common in unrelated languages, having occurred in the history of Classical Japanese, Classical Arabic and Proto-Celtic, for instance.
Some of the Chimakuan, Salishan, and Wakashan languages near Puget Sound lack nasal occlusives [m] and [n], as does the Rotokas language of Papua New Guinea. In some African and South American languages, nasal occlusives occur only in the environment of nasal vowels and so are not distinctive.
Formal Samoan has nasals /n ŋ/ and /t/ but only one word with velar [k]; colloquial Samoan conflates these to /ŋ k/. Ni‘ihau Hawaiian has [t] for /k/ to a greater extent than Standard Hawaiian, but neither distinguishes a /k/ from a /t/. It may be more accurate to say that Hawaiian and colloquial Samoan do not distinguish velar and coronal stops than to say they lack one or the other.