Alpha-channel: some bitmap formats can have transparent areas in them. (For example, the background might be transparent.) There are two types of bitmap transparency:

simple on-off transparency. This is the only type of transparency available in GIF bitmaps and in PNG bitmaps up to 256 colors.

"alpha-channel" or graduated transparency. This is variable between fully transparent and fully opaque. (Similar to the LX's transparency effects.) Alpha-channel is available for PNG true-color bitmaps.

Xara LX can import and export both simple and alpha-channel transparency.