Meaning:
bye-bye

Usage Example:
お婆ちゃんは最後に孫を抱き、満面の笑みで「あばあばねえ」と言った。 (Grandmother smiled and said aba aba as she gave her grandson a last hug.)

Notes:
baby talk for the word abayo which means “bye” (「あばよ」の幼児語)