From Minecraft Wiki
Count: Number of items stacked in this inventory slot. Any item can be stacked, including tools, armor, and vehicles. Range is -128 to 127. Values of 1 are not displayed in-game. Values below 1 are displayed in red.
Slot: The inventory slot the item is in.
Damage: The data value for this item. The name "Damage" comes from when only tools used this value, now many other items use this value for other purposes. For blocks, it is the 4-bit "block data" tag that determines a variant of the block. Defaults to 0.
id: Item/Block ID. If not specified, Minecraft changes the item to stone (setting ID to 1 and Damage to 0, and ignoring any existing Damage value) when loading the chunk or summoning the item.
tag: Additional information about the item, discussed more in the subsections of the item structure section. This tag is optional for most items.
CustomPotionEffects: The custom potion effects (status effects) this potion or tipped arrow has. A potion getting its effects from this tag will be named "Water Bottle". A tipped arrow will be named "Arrow of Splashing".
One of these for each effect.
Id: The numeric ID of the effect.
Amplifier: The amplifier of the effect, with level I having value 0. Negative levels are discussed here. Optional, and defaults to level I.
Duration: The duration of the effect in ticks. Values 0 or lower are treated as 1. Optional, and defaults to 1 tick.
Ambient: 1 or 0 (true/false) - whether or not this is an effect provided by a beacon and therefore should be less intrusive on the screen. Optional, and defaults to false. Due to a bug, it has no effect on splash potions.
ShowParticles: 1 or 0 (true/false) - whether or not this effect produces particles. Optional, and defaults to true. Due to a bug, it has no effect on splash potions.
Potion (since 15w31a): The name of the default potion effect. This name differs from the status effect name. For example, the value for an "Instant Health II" potion is "minecraft:strong_healing". A potion or tipped arrow getting its effects from this tag will be named with the proper effect.
CustomPotionColor: The item uses this custom color, and area-of-effect clouds, arrows, and splash and lingering potions use it for their particle effects. This color does not extend, however, to the particles given off by entities who ultimately receive the effect. The numeric color code are calculated from the Red, Green and Blue components using this formula: Red<<16 + Green<<8 + Blue. For positive values larger than 0x00FFFFFF, the top byte is ignored. All negative values produce white.