To orbit is to follow a circular or elliptical path around a central body. Usually a planet, moon or satellite is described as orbiting, but a child who has too much sugar can sometimes orbit around his parents in an annoying fashion.
The FDA was empowered by the United States Congress to enforce the Federal Food, Drug, and Cosmetic Act, which serves as the primary focus for the Agency; the FDA also enforces other laws, notably Section 361 of the Public Health Service Act and associated regulations, many of which are not directly related to food or drugs.
This branch interprets laws. Your officeholders that make laws are part of the legislative branch, along with institutions such as the Library of Congress. If you got a job as a court secretary in a federal tax court, you would be a federal employee in the judicial branch of government. The U.S. Postal Service. The U.S. Postal Service is a quasi-federal agency; Congress sets the rules that govern its operations but it receives no tax revenue.