I am a bit confused about how to classify the sound "w" in English. In some books I find that it's a bilabial and in some others that it is a velar! What is right? Can it be both? In fact yes the place of articulation involves both the lips and the velum!
From a narrow phonetic perspective, [w] in English involves raising and backing the tongue while protruding the lips, so from that point of view, "labiovelar" would be the best description, as Ivan Kapitonov said. However, we also like to reduce linguistic descriptions to less stuff. Thus one can also refer to that glide phonologically as a labial glide, a velar (or back) glide, or a bilabial glide (though adding "bi-" would be less than minimal, compared to simply "labial"). Some languages, such as French, have an additional glide type, labio-palatal ([ɥ] as in huite), which means that "labial" alone is insufficient for describing [w] in such languages. In English, we have fewer glides so we have more choices.
Languages can differ in how [w] behaves phonologically, even when there are only the glides [w, j]. In Chukchi for example, [w] behaves like a labial glide so that /ŋ/ becomes [m] before [w] and other labials. But in Sotho, nasal assimilation gives a velar nasal [ŋ] before [w]. A third possibility would be that [w] is treated distinctly from /p b m/ and /k g ŋ/, and could be treated like the labio-velar stops /kp gb ŋm/, which predicts the possibility of there being a language where nasals become [ŋm] before [w] (as well as /kp gb/). There don't seem to be any such cases, but labio-velar nasals are rare anyhow and languages with such sounds are not well studied. There isn't really much evidence telling us which analysis of [w] is best for English.
Yes, you've answered your question correctly. Keep it up.
On a consonant chart [w] would occur in both the labial column and the velar column.
That makes it a labiovelar (hyphenation optional) consonant, like Latin QU and Lushootseed k̉ʷ.
- Lat quinque '5' ['kʷinkʷe]
- Lu ck̉ʷaqid 'always' ['tsk̉ʷaqed]
Labiovelars are produced by simultaneous articulation, using different articulators.
Labialization is the phonetic process of rounding the lips while articulating a consonant.
This happens quite frequently to consonants; American English /r/ is rounded, for instance.
It's particularly easy to labialize a velar, because the simultaneous articulators are so far apart.
So labiovelars occur widely; labiovelar stops were prominent in Proto-Indo-European, for instance.