Liquids are
approximant consonants that are not classified as
semivowel (glides)
because they do not correspond phonetically to specific
vowels (in the way that, for example,
the initial [j] in English
yes corresponds to [i]).
The class of liquids can be divided into
lateral liquids and
rhotics.
[l] and [r] are typical liquids.
See Phonetics, Stop consonant, Fricative, Affricate.