From Tech Artists Wiki
An Address Mode is how a texture sampler reads a texture outside of the 0 to 1 range of texture coordinates. Address Modes can be specified in U, V, and W axes individually.
- Border: Takes a specified fill color that surrounds the texture (black by default). Note that when mipmapping, this color will interpolate into the 0-1 space.
- Clamp: Takes the edge pixels, and continues them on
- Mirror: Mirrors the texture
- Wrap: Repeats/tiles the texture