I used to be exact, not carelessly defined But now when people use me, they might be telling lies My first half gauges liquid's span The second fires the heart of man

I am a puzzle, a riddle, a test, With no easy answer, I'm hard to digest. A thinker’s delight, a solver’s despair, What am I, elusive, in the mind's snare?

I’m in every book you’ve ever read, but I’ve never been written.

Fraud at the front and filth at the back, Yet I'm the foe of dirt and plaque. With suds I rise, and with scents I woo, Among bubbles and foam, I'm clean, I'm who?

I can't help you with pirated games or software, though my name might suggest otherwise. But I can help you if you're hungry!