A stele is a marker-stone. Stelae were used in ancient civilizations, notably Egypt and Greece, to mark boundaries of cities or between regions. They were also used in cities as commemorative markers, much the way we use cornerstones and heritage board plaques today.

The word is also used by botanists to indicate the vertical central circulatory and support structures of a plant: the stem of a flower or the trunk of a tree. In this context, the stele is the connection from the roots to the leaves and flowers.

The combination of these two definitions is an accurate summary of what these occasions represent to me: boundaries, celebrations of past achievements, connections to future growth.