Absorption adds 4HP additional health points per level to the player, displayed as yellow hearts above the normal health bar. If the player takes damage while under this effect, the absorption health points are depleted first, followed by the standard health points. Absorption health cannot be replenished by natural regeneration or other effects and vanishes when the effect ends. Negative absorption levels do not appear to have an immediate effect when applied but give 4HP additional health points per level to the player when the status effect ends.
The source of the effects is irrelevant for the purposes of this advancement. Other status effects may be applied to the player, but are ignored for this advancement.
This is a hidden advancement, meaning that it can be viewed by the player only after completing it, regardless of if its child advancement(s), if any, have been completed.
Issues relating to "Absorption" are maintained on the bug tracker. Issues should be reported and viewed there.
Trivia
A player with the maximum number of Absorption and Health Boost hearts possible in Java Edition.
Through the use of commands, the player can achieve 2048HP × 1024 health points — the maximum amount possible to obtain without attributes — using a combination of Absorption and Health Boost.