What does “ein sof” mean in Hebrew?

This classic song about a baby brother ends every chorus the same way: ולשיר אין סוף — “and the song has no end.” אין סוף, literally “there is no end,” is more than a lyric. Fused into one word, אינסוף is Hebrew’s term for infinity — the one used in math class. And in Jewish mysticism, האין־סוף, “the Endless,” is Kabbalah’s name for God beyond all description.

אין is the mirror of יש (“there is”): יש סוף “there’s an end,” אין סוף “there is none.” The everyday sigh אין סוף לזה — “there’s no end to this” — fits laundry as well as paperwork. In the song, the baby brother can’t walk yet but can already drum and sing — which is exactly why the song never ends.