Most moms say this as a way to get their kids to mind their Ps and Qs. But really the magic word(s) are "HEY THIS IS LIBRARY" It means "mind your Ps and Qs" or "Say please" to get children to say their manners.
Someone who is addicted to obtaining money and building wealth. A money addict and fanatic. Breadheads often work more than one full-time job, and some even participate in illicit activities to "obtain the bread".