approximant

This term belongs to the specialized domain of phonetics and linguistics. It describes a sound that occupies a middle ground between a vowel and a true consonant. The defining characteristic is the lack of friction; the tongue or lips approach the roof of the mouth or each other, but they do not touch or get close enough to cause the air to hiss or whistle. In practical usage, it is a technical descriptor used by linguists to categorize sounds like l and r. It carries a neutral, scientific connotation and is almost never used in casual conversation unless discussing the mechanics of speech production.