Vanitas is the Latin for vanity, in the sense of emptiness or a worthless action. 'Vanity of Vanities, saith the preacher, all is vanity' (Ecclesiastes 12: 8). The implication of these words from the Old Testament is that all human action is transient in contrast to the everlasting nature of faith.
A vanitas is a particular type of still life painting in which objects symbolically refer to such a theme. For example, in Steenwyck's 'Allegory' in the Collection, objects which suggest human achievements, like the book and instruments, are related to reminders of mortality: the lamp which has been snuffed out and the skull. (See the entry for Memento Mori.)