またね [mata, neh] means "Again, non?" and is used as a "See you later, See you again, A Tout a L'heure"-like expression for use with friends and those of the same age. じゃあね [ja'a, ne] is a short-hand for this, and is short for 「じゃあ、またね」 [ja'a mata, neh] Meaning "Well, alright, see you again [later]." One can also use the phrase 「また会いましょう」 "mata aimashо̄" to say "Let us meet again" with a polite-flair at the end, suitable for use with elders and teachers alike.