Excel’s ISBLANK function is one of a group of “Information Functions” that can be used to find out information about a specific cell.
The ISBLANK function's job is to check to see if a certain cell is empty or not. If the cell is empty, a value of TRUE is returned by the function. If the cell contains data of any kind - such as a text label, a number, or a date - a FALSE value is returned.
Since Excel does not distinguish between an empty cell and one containing a zero, errors can sometimes occur if a blank cell is mistakenly included in a formula. The ISBLANK function can be used to avoid introducing such errors into a spreadsheet.
To find out all the details of using this function read the short article on the Excel 2007 ISBLANK Function.