Splash Potion

Splash potions are a variant of potions that can be thrown.

Brewing
Splash potions are brewed by adding gunpowder to a normal potion.

Natural generation
One splash potion of weakness can be found in a brewing stand inside an Igloo basement.

Filling bottles
Using a glass bottle on a cauldron that contains splash potion will turn it into a bottle of that splash potion. Using a glass bottle on a cauldron also removes $1/3$ of that cauldron's contents.

Brewing
Lingering potions are brewed by adding dragon's breath to a splash potion.

Using
Splash potions are thrown by them. On impact they explode, applying status effects to nearby entities. The bottle is lost, unlike drinkable potions. Entities within an 8.25×8.25×4.25 cuboid centered on the thrown potion at impact and within 4 blocks euclidean distance of the thrown potion at impact are affected.

The farther away the entity is from the center of the explosion, the lesser the imbued effect. For effects without duration such as Healing or Harming, the potency of the effect reduces linearly from 100% on a direct hit to 0% at 4 blocks' distance. For effects with duration, the effect has full potency but the duration decreases linearly on the same scale (rounded to the nearest $1/20$ second), with no effect being applied if the duration would be 1 second or less. Throwing a potion at an entity's head will maximize the duration, compared to the feet.

Splash water bottles
Splash water bottles have no effect on entities, but will put out fire in the block hit and the four blocks horizontally surrounding it.

A splash water bottle will deal damage to an enderman or a blaze. An enderman will teleport away before being hit, but can still be caught in the effect radius if targeted indirectly.

Filling cauldrons
Using a splash potion on a cauldron will add one level of that potion to the cauldron. Attempting to add a splash potion to a cauldron with water, dyed water or a non-matching potion will empty the cauldron and create an explosion sound (but no actual explosion).

Data values
Splash potions when thrown have entity data which define various properties of the entity. Their entity ID is.

In Bedrock Edition, this is a distinct entity from the thrown lingering potion. In Java Edition, this is the same entity, and the stored  tag determines whether it is a splash or a lingering potion.

Trivia

 * If endermen are targeted directly by a splash potion, they will teleport away before the potion can take effect. However, if they are caught in the splash radius of a potion not aimed at them, they will be affected.
 * If killed by a splash potion of harming, the death message would be:  was killed by magic