Various tools use the Bleed, Margin, and Padding terms differently. This should be made consistent.
My understanding of the correct usage is this:
- Margin: empty space around items, such as UVs, in order to allow room for texture padding.
- Padding: generated pixels within the margins around the island borders of textures to prevent bleeding.
- Bleeding: the overlapping of UVs onto the wrong texturespace, generally due to downsampling, that results in seams
Polycount has a good Wiki entry on Edge Padding: http://wiki.polycount.com/EdgePadding