It is a term used in Botany, to refer to a part of the flower. It's a modified sepal. It is a sepal or a leaf that forms a chalice of a flower, which has the same coloration of this.
Tepal: m. (Bot. ) Each of the sheets forming simple perianth of haploclamideas flowers. Appearance intermediate between typical, as hyacinth and Lily a sepal and a petal.