In phonetics, a trill is a consonantal sound produced by vibrations between the active articulator and passive articulator. Standard Spanish ⟨rr⟩ as in perro, for example, is an alveolar trill.
A trill is made by the articulator being held in place and the airstream causing it to vibrate. Usually a trill vibrates for 2–3 contacts, but may be up to 5, or even more if geminate. However, trills may also be produced with only one contact. While single-contact trills are similar to taps and flaps, a tap or flap differs from a trill in that it is made by a muscular contraction rather than airstream. Individuals with ankyloglossia may have issues producing the trill sound.