1. The document is a geometry drill from December 17, 2013 that contains problems about triangle properties like perpendicular bisectors, angle bisectors, circumcenters, medians, altitudes, centroids, and orthocenters. 2. Key terms defined include median, centroid, altitude, and orthocenter of a triangle. 3. The document provides explanations of medians, altitudes, centroids, and orthocenters of triangles and their properties.