can someone tell what the heck that is

Retical expansion with little recoil per shot I think, I dunno if I am right though

Well, bloom can mean many things.
Bloom - Shader effect
Bloom - Something flowers do
Bloom - The reticle expanding and retracting to encourage timing shots for better accuracy
Bloom - A bunch of Jellyfish (like a murder of crows - a bloom of jellyfish)
Bloom - A chunk of steel that gets hammered out from an ingot
Bloom - “Love is in bloom”