For transportation purposes, materials are fissile only if DOT says so. This discussion will deal with uranium and its isotopes. Note that natural and depleted uranium are specifically excluded from this definition. Look at the definition of enriched uranium in 173.403. Enriched material has a higher percentage of the U-235 isotope than what can be found in natural uranium.
Enrichment can take place at different points in a process, and can be at different levels.
Around the DOE complex, you will find natural uranium, depleted uranium, and enriched uranium. It is extremely important to determine what kind of uranium you are shipping, as the shipping requirements will differ greatly. Additionally, if your material is enriched uranium, you will need to know the enrichment level. Unfortunately, the typesetting for this table is not all that it could be. The reader has to be particularly diligent when looking at the entries for uranium, lest they be led astray by the misaligned print.