Tepals are elements of the perianth, or outer part of a flower, which includes the petals or sepals. The term "tepal" is applied when all the segments of the perianth are of similar shape and color, or undifferentiated. When different types of organs can be distinguished, they are referred to as sepals and petals. The term was first proposed by Augustin Pyramus de Candolle in 1827. De Candolle used the term perigonium (or perigone) for the tepals collectively; today this term is used as a synonym for "perianth".

Undifferentiated tepals are thought to be the ancestral condition in flowering plants, for example, Amborella, which is thought to have separated earliest in the evolution of flowering plants, has flowers with undifferentiated tepals. Distinct petals and sepals would therefore have arisen by differentiation, probably in response to animal pollination. In typical modern flowers, the outer or enclosing whorl of organs forms sepals, specialised for protection of the flower bud as it develops, while the inner whorl forms petals, which attract pollinators.

In some plants the flowers have no petals, and all the tepals are sepals modified to look like petals. These organs are described as petaloid, e.g. the sepals of hellebores.

Undifferentiated tepals are common in monocotyledons. In tulips, for example, the first and second whorls both contain structures that look like petals. These are fused at the base to form one large, showy, six-parted structure. In lilies the organs in the first whorl are separate from the second, but all look similar, thus all the showy parts are often called tepals.