It is a bitwise operator, here is an explanation taken from this page.
This is the zero-fill right shift
operator which shifts the binary
representation of the first operand to
the right by the number of places
specified by the second operand. Bits
shifted off to the right are discarded
and zeroes are added on to the left.
With a positive number you would get
the same result as with the
sign-propagating right shift operator,
but negative numbers lose their sign
becoming positive as in the next
example, which (assuming 'a' to be
-13) would return 1073741820:
Watch out though, bitwise operators are pretty slow in JavaScript.
