PPT Slide
Focus: One of two unique points along the semimajor axis. The primary body lies at one of these foci.
Primary Body: The most massive body in a system. For now, it is to be taken to be considerably more massive.
Secondary Body/Bodies: The body/bodies or lesser mass. For now, it/they is/are to be taken to be considerably less massive.
Peripase: The point in the orbit located closest to the primary body.
Apoapse: The point in the orbit located farthest from the primary body.