Adverb
that is to say; in other words
Source: WordNetSome manuscripts have the gloss id est terra vini. Source: Internet
Virgil gives Laocoön the famous line " Equō nē crēdite, Teucrī / Quidquid id est, timeō Danaōs et dōna ferentēs ", or "Do not trust the Horse, Trojans / Whatever it is, I fear the Greeks even bearing gifts." Source: Internet