(noun) - A vanitas painting was a particular type of still life immensely popular in the Netherlands (and Paris, to a lesser extent), beginning in the 17th century.
The phrase comes to us courtesy of a Biblical passage in Ecclesiastes, in which the Hebrew word "hevel" was incorrectly taken to mean "vanity of vanities". But for this slight mistranslation, the term would rightfully be known as a "vapor painting". Be that as it may ...
A vanitas painting, while possibly containing lovely objects, always included some reference to man's mortality - most often a human skull (with or without other bones), but also by way of burning candles, soap bubbles or decaying flowers. It was meant not only to be a work of art, but also to carry an important moral message: Trivial pleasures of life are abruptly and permanently wiped out by death, so don't get too carried away during your earthly time, Bub.
It is doubtful that this genre would have been popular had the Counter-Reformation and Calvinism not propelled it into the limelight.
 Hans J. Van Miergroet: 'Vanitas', Grove Art Online, (Oxford University Press, Accessed 7 January 2005), http://www.groveart.com