The word is also used to describe a cultural complex of behaviours that the bereaved participate in, or are expected to participate in. In the Western world, these behaviours took their most extreme forms in England during the reign of Queen Victoria.
Victoria herself may have had much to do with the practice, due to her long and conspicuous grief over the death of her husband, Prince Albert. Women bore the greatest burden of these customs. They involved wearing heavy, concealing, black clothing, and the use of heavy veils of black crêpe. The entire ensemble was colloquially known as widow's weeds.
Widows were expected to wear special clothes to indicate that they were in mourning for up to four years after the death. To remove the costume earlier was thought disrespectful to the decedent, and if the widow was still young and attractive, sexually promiscuous. Those subject to the rules were slowly allowed to re-introduce conventional clothing at different time periods; stages were known by such terms as "full mourning", "half mourning", and similar terms.
What was a voluntary statement of an attitude of deep grief on the part of the Queen became an officious and oppressive etiquette. Men were much less burdened by all of this than women were. Men were expected to dress in dark colours for up to a year after a death in the family.
Mourning clothes of the sort our grandmothers rejected have currently staged a minor comeback and are popular items of vintage clothing.