1. means "I don't know" in French.
2. also one of three answers you give your French teacher when he/she asks you a question that you don't know the answer too or are just too lazy to answer. (the others being "oui" and "non")
M/Mme/Mlle whoever: "Qu'est-ce qui s'est passé dans les chapitres que tu as lu hier?"
Student: "Ehh...je ne sais pas...mais c'était très intèressant?"
("What happened in the chapters that you read yesterday?" "Eh...I don't know...but it was very interesting?")
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".