Visibility: Object is completely obliterated
The property "Object is completely obliterated" detects objects that are completely obliterated by other objects (and are thus not visible on the page). An object is considered completely obliterated in this context if at least one other opaque object (i.e. neither overprinting nor transparent) above it fully overlaps it, thus completely suppressing rendering of that object.
For detecting partial obliteration see the article Visibility: Object is partially obliterated.
The "Filter" option defines the set of objects for which it shall be determined whether they are completely obliterated.
The example below makes use of the check Object is completely obliterated.kfpx and the PDF file three red rectangles, one half obliterated, one fully obliterated.pdf which are available for download:
The page shown in the screenshot below contains three evenly spaced red squares, where the middle one is half obliterated, and the rightmost one is fully obliterated (and thus not visible).
It can be seen below how the completely obliterated (and thus invisible) red square on the right is detected.