On Facebook my friends have been putting null as the description for their picture, what does null mean?
that means that the page wasnt done loading when they typed the caption for the picture, and "null" was entered, because that is computer database terminology for "nothing" or "empty"
it's a glitch in essence - it doesnt really mean anything special that you are missing
without value, effect, consequence, or significance, being or amounting to nothing; nil; lacking; nonexistent, nada
Lots of dictionaries online too