Supplied Diameter also referred to often as minimum supplied diameter is the minimum inner diameter of the heat shrink as supplied by the manufacturer. This means that if you order a 1/4" supplied diameter the minimum supplied inner diameter of that heat shrink will be 1/4". It also means it may vary slight over that 1/4" minimum.
Recovered Diameter or maximum recovered diameter is the maximum inner diameter that the heat shrink will shrink down to. Even if the heat shrink mentioned above was slightly over the 1/4" supplied diameter it would shrink to at least the maximum recovered inner diameter specification when heated.
You can also use these two measurements to get your Shrinkage Ratio. This ratio is the Supplied diameter over your recovered diameter. So if you had a supplied diameter of 2 inches and a recovered diameter of 1 inch you would have a 2 to 1 shrinkage ratio.