Minecraft wiki entry for Enchanting, associated text: Max Level: Maximum levels for enchantments vary, but the game can comprehend up to 32-bit integer values (−231 to 231−1). Exceeding this value results in an overflow, and eventually resets itself to 0.
Primary Items: The items that can receive the enchantment legitimately in Survival mode by using an enchanting table. Items of any material can be enchanted (some more easily than others – see Enchantment mechanics).
Secondary Items: Items that, in Survival mode, cannot receive the enchantment from an enchanting table but can from an enchanted book with an anvil.
Weight: Relative probability of the enchantment being offered.