HappY tensing

From Teflpedia

happY tensing is pronouncing unstressed final lax /ɪ/ as [iː].

Happy may be pronounced [ˈhæpiː] with happY tensing and [ˈhæpɪ] without it. In a broad notation its arbitrary to use /iː/ or /ɪ/. In Teflpedia we use /iː/: /ˈhæpiː/

See Pronunciation exercises: /ɪ/ vs /iː/ § Unstressed syllable.