Mourning is the process of and practices surrounding death related grief. The word is also used to describe a cultural complex of behaviours in which the bereaved participate or are expected to participate. Customs vary between different cultures and evolve over time, though many core behaviors remain constant. Wearing dark, sombre clothes is one practice followed in many countries, though other forms of dress are also seen. Those most affected by the loss of a loved one often observe a period of grieving, marked by withdrawal from social events and quiet, respectful behavior. People may also follow certain religious traditions for such occasions.