What is the X in X-mas?
plural schemata, 1796, in Kantian philosophy ("a product of the imagination intermediary between an image and a concept"), from Greek skhema (see scheme (n.)). Meaning "diagrammatic representation" is from 1890; general sense of "hypothetical outline" is by 1939.
schema sche·ma (skē'mə)
n. pl. sche·mas or sche·ma·ta (skē-mä'tə, skĭ-māt'ə)
A diagrammatic representation; an outline or a model.
A pattern imposed on complex reality or experience to assist in explaining it, mediate perception, or guide response.