When you keep an eye on someone, that's supervision. Small children require supervision when they're swimming, and a middle school math class needs supervision while they're taking a quiz.
To watch over and keep people (or animals) safe, or to watch and manage them while they work, is to supervise them. The act of doing this is supervision. If your boss lets you work without supervision, that means that she doesn't feel the need to observe you while you get your job done. Supervision and supervise stem from the Latin roots super, "over," and videre, "to see."