Polite form of だ (da), after uninflecting parts of speech: to be / After the plain past or nonpast form of -i adjectives (or nonstandardly verbs), to form the polite ending.

is, am, are

(Kyūshū or informal) It is indeed so. / Yes.

Polite form of のです (no de su, used to indicate strong assertion).

used to give an explanation or reason / used to give an emphasis or a special sense

(polite) Polite form of なのだ (na no da, used to indicate strong assertion).

(formal) Alternative form of だから (da kara)

Yes / It seems that (adjective/adjectival phrase) / That's right

seems like; looks like; I hear that

is expected to ~; should ~; supposed to ~