A "4x4" is a particular
cut of
lumber in the
United States. More
precisely, it was once a
cut of
lumber four inches wide and
four inches thick. Currently, however, it is
three and a
half by
three and a
half inches. The
length of the board is not specified.
"4x4" is
spoken as "four by four" and
refers to a
board meeting this
specification.