This paper presents an interpretation of the term "concept," as the term is used in Ausubelian learning theory to define the unit of organization in cognitive structure. Several facets of a concept are described, a model of a concept is presented, and the model is then discussed and criticized as a heuristic device to aid educators in understanding certain aspects of teaching and learning. The latter portion of the paper discusses the types of expertise considered necessary for facilitating meaningful learning, culminating in a simplified model of curriculum and instruction. (CS)