The term labiovelar is ambiguous. It may mean labial-velar (a consonant made at two places of articulation, one at the lips and the other at the soft palate), or it may mean labialized velar (a consonant with an approximant-like secondary articulation).
When the manner of articulation is a plosive, nasal stop, or fricative, these are quite different. Labialized velars include , which are pronounced like a but with rounded lips. Labial-velars are less common, occurring principally in West and Central Africa, and include , which are pronounced like a simultaneous [k] and [p], [ɡ] and [b], and [ŋ] and [m]. Labial-velar fricatives are not thought to be possible, since it is difficult to control the airstream precisely enough to produce frication at two places of articulation, and in any case the sound of the forward articulation would mask the other. ([ʍ] is not actually a fricative, but rather a voiceless approximant, and in any case is labialized, not labial-velar.)
The most common labiovelar consonant is the voiced approximant [w]. This is normally a labialized velar, as is its vocalic cousin [u]. (Labialization is called rounding in vowels, and a velar place is called back.) However, languages such as Japanese and perhaps the Northern Iroquoian languages have something closer to a true labial-velar approximant, where the lips come together. In close transcription, the symbol [w] may be avoided in such cases, or it may be used with an under-rounding diacritic, as [w̜].
[w] and its voiceless equivalent are the only labialized velars with dedicated IPA symbols:
|voiceless labialized velar approximant||English||which||[ʍɪtʃ]1||'which'|
|voiced labialized velar approximant||English||witch||[wɪtʃ]||'witch'|
1In dialects that distinguish between which and witch.
The voiceless approximant is traditionally called a "voiceless labial-velar fricative", but true doubly articulated fricatives are not known to be used in any language, as they are quite difficult to pronounce and even more to aurally distinguish. (However, very occasionally the symbol [ʍ] is used for a labialized velar fricative, [xʷ]. This usage is not approved by the IPA.)