Premium - Consistency in the movement, pattern, and color of the stone. It is as close to flawless as nature allows.
Standard - The stone will have an overall consistency in color. Although there can be minor changes in color periodically. Patterns can also change. There can be changes in the movement.
Commercial - There will be Color changes, Pattern changes, Patching, and/or the Movement will not be consistent.
Some places sell commercial that has cracks, chips, holes, or fissures that will have been repaired. stay away from these. If you are buying for your home pay the extra for premium It is worth it in the end. Most people enjoy Brazilian or Indian the most, due to the vibrant colors and usually better quality of the stone and the finish.