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?")