The \multicolumn is command is
used to make an entry that spans several columns.
It is useful for making table headings which span several columns, or
for changing the positioning of the heading for a single column (the
pos argument in \multicolumn overriding that of
the \tabular value, for example).
The first mandatory argument, cols, specifies the number of columns to
span. The second mandatory argument, pos, specifies the formatting of
the entry;
c for centered
l for flushleft
r for flushright
The third mandatory argument, text,
specifies what text is to make up the entry.
\multicolumn must either begin a row or be placed immediately
after an &.