**Envelope (mathematics)**

In geometry, an **envelope** of a family of curves in the plane is a curve that is tangent to each member of the family at some point. Classically, a point on the envelope can be thought of as the intersection of two "adjacent" curves, meaning the limit of intersections of nearby curves. This idea can be generalized to an envelope of surfaces in space, and so on to higher dimensions.

Read more about Envelope (mathematics): Envelope of A Family of Curves, Envelope of A Family of Surfaces, Generalisations

### Famous quotes containing the word envelope:

“... all my letters are read. I like that. I usually put something in there that I would like the staff to see. If some of the staff are lazy and choose not to read the mail, I usually write on the *envelope* “Legal Mail.” This way it will surely be read. It’s important that we educate everybody as we go along.”

—Jean Gump, U.S. pacifist. As quoted in The Great Divide, book 2, section 10, by Studs Terkel (1988)