Et måltid is indefinite. And måltidet is definitive. The common way in Norwegian is to put the indefinite article (en, ei, et) at the end of the word to make it definitive. En mann - mannen. Ei dame - dama (the ei turns into a). Et måltid - måltidet

In plural most nouns gets -er in indefinite and -ene in definitive. But there is a long list over those that don't.