What does the ⌧ button do? I just bought a wired mac keyboard. Where I would expect numlock to be, it has a key with this mysterious symbol on:

⌧
(a rectangular box with a cross through it)

What is this button?
This is Clear key.

From Wikipedia:


  A Clear key, instead of a Num Lock key, on models with full numeric keypads, as these are dedicated to numeric input and not generally used for cursor control. In Unicode, the Clear key is represented by U+2327 ⌧ x in a rectangle box, defined as "clear key"