What does "dreg" mean?

Dreg: Corrupt or defiling matter contained in a liquid, or precipitated from it; refuse; feculence; lees; grounds; sediment; hence, the vilest and most worthless part of anything; as, the dregs of society. We, the dregs and rubbish of mankind. Dryden. Note: Used formerly (rarely) in the singular, as by Spenser and Shakespeare, but now chiefly in the plural.