The visibility property specifies whether or not an element is visible. But unlike setting 'display' to 'none', if you set 'visibility' to 'hidden' the hidden element will still take up the same space on the page - it just won't be visible.
Value
Description
visible
The element is visible. This is default
hidden
The element is invisible (but still takes up space)
collapse
Only for table elements. collapse removes a row or column, but it does not affect the table layout. The space taken up by the row or column will be available for other content. If collapse is used on other elements, it renders as 'hidden'
Visibility
The visibility property specifies whether or not an element is visible. But unlike setting 'display' to 'none', if you set 'visibility' to 'hidden' the hidden element will still take up the same space on the page - it just won't be visible.
Themeover CSS Reference
Online CSS References: Visibility
Online CSS Tutorials: Visibility