An environment map is a set of image files that are mapped to the six faces of an imaginary cube surrounding a model (or environment). The way that environment maps are treated depends on settings in the Environment Manager dialog.
A typical usage of environment mapping would be to show reflections of an outdoor scene, using images of the sky for the top and sides and a ground image for the ground.
The imaginary environment cube is constructed slightly beyond the extents of the design file and is not directly visible, unless Visible Environment also is enabled. Where Visible Environment is not enabled, it can be seen only in reflections. The environment cube also can be rendered as part of a view if you create a totally transparent cube that surrounds the entire model.
If a model with an environment map(s) is to be animated, it is advisable to create geometry that defines the extents of the portion to animate. This will prevent the environment map(s) from drifting.