| In phonetics, a stop which is both egressive and glottalic. What this means in detail is that as well as a temporary stoppage somewhere in the mouth (making it a P or T or K or whatever, depending on where that primary stoppage is), there is also a stoppage of the glottis (in the larynx), which is moved briefly upward to compress the trapped air. The primary stoppage in the mouth is then released as normal, and the consonant bursts out more sharply.
They are also called glottalized stops. It is similar to having a glottal stop attached to the consonant, though not the same: if I read it right, the Mayan language Tzotzil for one distinguishes these possibilities.
The ejectives are normally written with an apostrophe, e.g. p' t' ts' ch' k' q'. They are common in both Georgian and the North Caucasian languages; they occur in Amharic in Ethiopia; in Zulu and Xhosa; and in many American languages. The Nigerian language Hausa has ejective ts and k. Because Hausa also has a normal (plosive) k, the ejective one is written in its alphabet with the top of the k curling over to the right.
In both Georgian and Zulu they contrast with aspirated stops. (Unfortunately in transliterating Georgian sometimes the apostrophe is used for the aspirated one of the pair.) In Quechua you get all three kinds, plain, aspirated, and ejective.
They ejectives are (virtually?) never voiced. Voicing would require vibrating the glottis, and this is close to impossible when stretched upward. Contrast these with implosives, which are also glottalic, but are released downward into the throat. | 
