A stop is a type of consonant which is formed by stopping the air completely in the mouth (e.g., by closing the lips or blocking the air with the tongue at the alveolar ridge, then releasing it suddenly. The release is sometimes accompanied by a puff of air (called aspiration).
Stops are sometimes called plosives – they mean the same thing, but stop focuses on the stopping part, plosive focuses on the release.
The most common stops are [p, b, t, d, k, g] plus retroflex stops [rd, rt] and glottal stops. Nasal sounds (like [m, n, ng, ny]) are sometimes called nasal stops, as they also block the air completely in the mouth, but don’t release in the same way as oral stops.
Stops can be voiced or voiceless (see voicing) but in many Aboriginal languages this doesn’t change the meaning.