DAU = daily user? That's funny, in German tech-slang DAU is short for a really dumb/ignorant user. (DAU = "dümmster anzunehmender User", as a word play on GAU = "größter anzunehmender Unfall" = "maximum credible accident")
Yes - it is short for daily active user and often compared to WAU(weekly) and MAU(monthly) to get rough idea of engagement. The apps with the highest DAU are usually really silly games, though, so maybe you are on to something there...