colspan

This attribute contains a non-negative integer value that indicates for how many columns the cell extends. Its default value is 1; if its value is set to 0, it extends until the end of the <colgroup>, even if implicitly defined, that the cell belongs to. Values higher than 1000 will be considered as incorrect and will be set to the default value (1).

Note: 
In HTML5 this attribute only accepts values greater than zero since it must not be used to overlap cells. Besides, Firefox is the only browser to support the 0 value as defined in the HTML 4.01 specification.
