names - Why is it called "Zos Chanukah"

Why is the eighth, and last, day of Chanukah called "Zos Chanukah" and what is it significance?

Answer

The eighth day of Chanukah contains the Torah reading including the sum total (Numbers 7:84) of all the tribes' leaders' dedication offerings. So the phrase used is "zos chanukas hamizbeach", this was the dedication/inauguration, and the eighth day of Chanukah is then known as "zos chanukah" or "this is chanukah." It has the longest Torah reading of all 8 days.

In Hassidic thought it has significance because it's the wrap-up of the holiday, as if to say "this represents how our chanukah went this year"; in some schools of Hassidic thought it's also seen as an extra-last-last chance for final judgment from the High Holidays (something like "the verdict is written on Rosh HaShanah and sealed on Yom Kippur ... but the book isn't closed until Hoshanah Rabba, and isn't put back on the shelf until Zos Chanukah" ... however you interpret that).