Many objects, beliefs and customs can be traditional. Rituals of social interaction can be traditional, with phrases and gestures such as saying "thank you", sending birth announcements, greeting cards, etc. Tradition can also refer to larger concepts practiced by groups (family traditions at Christmas), organizations (company's picnic) or societies, such as the practice of national and public holidays. Some of the oldest traditions include monotheism (three millennia) and citizenship (two millennia). It can also include material objects, such as buildings, works of art or tools.