An Envelope is a thin paper container formed by folding a sheet of paper and securing the edges, and is the major staple consumable of a letterpost service.
The envelope of an E-mail contains the information used for routing and is passed along the E-mail without being part of the actual message.
In science:
An Envelope is a mathematical Curve , Surface , or higher dimensional object defined as being Tangent to a given family of lines or curves (or surfaces, or higher dimensional objects, resp.).
