Vowel hiatus
Hiatus [haɪˈeɪtəs] in linguistics is the separate pronunciation of two adjacent vowels, sometimes with an intervening glottal stop. In poetic metrics, hiatus can also refer to the failure of two vowels straddling a word boundary to coalesce, for example by elision of the first vowel.
Many languages disallow hiatus, avoiding it either by deleting or assimilating the vowel, or by adding an extra consonant. In particular, some (but not all) non-rhotic dialects of English insert an /r/ to avoid hiatus after many vowels.
One of the languages which demands hiatus is Swahili. Also, 'hiatus' is one of the few English words which hiatus applies to.