Guttural speech sounds are those with a primary place of articulation near the back of the oral cavity, especially where it's difficult to distinguish a sound's place of articulation and its phonation. In popular usage it is an imprecise term for sounds produced relatively far back in the vocal tract, such as German ch or the Arabic ayin, but not simple glottal sounds like h. A 'guttural language' is a language that has such sounds.
As a technical term used by phoneticians and phonologists, it has had various definitions. The concept always includes pharyngeal consonants, but may include velar, uvular or laryngeal consonants as well. Guttural sounds are typically consonants, but murmured, pharyngealized, glottalized and strident vowels may be also considered guttural in nature. Some phonologists argue that all post-velar sounds constitute a natural class.
The word guttural literally means 'of the throat' (from Latin guttur, meaning throat), and was first used by phoneticians to describe the Hebrew glottal [ʔ] (א) and [h] (ה), uvular [χ] (ח), and pharyngeal [ʕ] (ע).
The term is commonly used non-technically by English speakers to refer to sounds that subjectively appear harsh or grating. This definition usually includes a number of consonants that are not used in English, such as epiglottal [ʜ] and [ʡ], uvular [χ], [ʁ] and [q], and velar fricatives [x] and [ɣ]. However, it usually excludes sounds used in English, such as the velar stops [k] and [ɡ], the velar nasal [ŋ], and the glottal consonants [h] and [ʔ].
In popular consciousness, languages that make extensive use of guttural consonants are often considered to be guttural languages. English-speakers sometimes find such languages strange and even hard on the ear.
Some of the languages that extensively use [x], [χ], [ʁ], [ɣ] and/or [q] are:
In addition to their usage of [q], [x], [χ], [ʁ] and [ɣ], these languages also have the pharyngeal consonants of [ʕ] and [ħ]:
In French, the only truly guttural sound is (usually) a uvular fricative (or the guttural R). In Portuguese, [ʁ] is becoming dominant in urban areas. There is also a realization as a [χ], and the original pronunciation as an [r] also remains very common in various dialects.
In Russian, /x/ is assimilated to the palatalization of the following velar consonant: лёгких [ˈlʲɵxʲkʲɪx] (help·info). It also has a voiced allophone ɣ, which occurs before voiced obstruents. In Romanian, /h/ becomes the velar [x] in word-final positions (duh 'spirit') and before consonants (hrean 'horseradish'). In Czech, the phoneme /x/ followed by a voiced obstruent can be realized as either [ɦ] or [ɣ], e.g. abych byl [abɪɣ.bɪl].
In Kyrgyz, the consonant phoneme /k/ has a uvular realisation ([q]) in back vowel contexts. In front-vowel environments, /g/ is fricativised between continuants to [ɣ], and in back vowel environments both /k/ and /g/ fricativise to [χ] and [ʁ] respectively. In Uyghur, the phoneme /ʁ/ occurs with a back vowel. In the Mongolian language, /x/ is usually followed by /ŋ/.
The Tuu and Juu (Khoisan) languages of southern Africa have large numbers of guttural vowels. These sounds share certain phonological behaviors that warrant the use of a term specifically for them. There are scattered reports of pharyngeals elsewhere, such as in the Nilo-Saharan, Tama language.
In Swabian German, a pharyngeal approximant [ʕ] is an allophone of /ʁ/ in nucleus and coda positions. In onsets, it is pronounced as a uvular approximant. In Danish, /ʁ/ may have slight frication, and, according to Ladefoged & Maddieson (1996), it may be a pharyngeal approximant [ʕ]. In Finnish, a weak pharyngeal fricative is the realization of /h/ after the vowels /ɑ/ or /æ/ in syllable-coda position, e.g. tähti [tæħti] 'star'.