SandBox 5 Points Defition :
1)- The ability to have a lasting impact on the game world
(building, teraforming, cultivating, etc.)
2)- Free-Form Character Development.
(Custom Cross-Classing, No Classes, Shifting Character Archetypes).
3)- Intricate Crafting System.
(Non-instanced construction of housing and facilities, collectable and refinable resources, Majority of equipment and use items able to be player made and modified).
4)- Open-ended gameplay.
(no fixed path of progression. Questing and storyline not directly tied to progression. No singular end-game objectives. Skills unrelated to combat level).
(factions, alliances, guilding and politics in general determined by the players often with player-base emergent systems of in game government. Economy maintained by the supply and demand of goods/wears/materials that are obtained/created/modified by the players and sold to the players).
In my opinion these factors are the primary (or at least major) definatives of the SandBox Sub-Genre of MMORPGs. And, should an MMORPG by large majority employ (4-5) these factors as part of it's aproach over a Themepark approach I consider the game to be Sandbox in Nature. Should a game employ a small majority/large minority of these factors in it's approach (3 or less). Leaving the rest of the 5 definative points to the Themepark side of things. I will consider it Sandpark (hybrid) in nature [as in: possessing a fairly balanced amount of features from both genres].