down tack

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun phonetics The IPA diacritic of primary articulation: < ˕ >, used to denote a lowered phone; for vowels, the diacritic denotes a slightly more open utterance; for consonants, it moves the point of articulation one step forward in this chain: nasal → plosive → fricative → approximant → trill → tap, flap → lateral fricative → lateral approximant → lateral flap.