Uvular consonants are articulated further back in the mouth than velar consonants are. Most uvular consonants are either stops or fricatives, but a very small number of languages use them as nasals, trills, or approximants.
Uvular consonants are found in many African and Middle-Eastern languages, most notably Arabic, and Native American languages, as well as the letter "r" in French and German.
The unvoiced uvular stop is expressed as "q" in most transliteration schemes, and is pronounced like a "k" with the middle of one's tongue against the soft uvula rather than the velum. The most familiar use will doubtless be in the transliteration of Arabic place names to English (such as Qatar and Iraq), though most English speakers pronounce the sound incorrectly as "k."
The voiced equivalent of "q" is much rarer, and is generally expressed as "G." It sounds like a "g" articulated in the same position as "q."
The unvoiced uvular fricative is also exceedingly rare, and is generally transliterated as "qh." It sounds like the "kh" (represented in IPA as "x") in German, Russian, or Arabic, only articulated on the uvula.
The voiced uvular fricative is much more common, and is generally transliterated either "r" or "Gh." It is found in French, German, Hebrew, and Arabic, and sounds like a voiced version of "qh." If you have heard a French or German individual speak English before, you will doubtless have noticed their pronunciation of the letter "r." That is the voiced uvular fricative.
