Meanings
colloquialunwell, queasy, poorly, ill
Mir ist mau.I feel queasy/ill/poorly.
colloquialdisappointing, bad, meagre (below expectations, either in quantity or quality, though typically not catastrophic)
Die Lage ist mau.The situation is bad.
2 more meanings
Adverb
colloquialbadly, bad
colloquialslack
Die Geschäfte gehen mau.Business is slack.
Examples
GermanEnglish
Manche sind schlau, manche mau.Some are wise, some are otherwise.