A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
For example:
Let's say you have a drop-down in B3, with source range =$K$1:$K$6
You do not want it to be filled in unless B2 is filled in.
Change the source to
=IF(B2="", $Z$1, $K$1:$K$6)
where Z1 is an empty cell (any empty cell will do), and clear the check box 'Ignore blank'.