Bloom is a stat on weapons. It is similar to recoil. The lower the Bloom, the better.

Bloom is a game mechanic in the video game Defiance

Bloom is the rate at which your crosshairs/reticule widens during sustained fire. The higher the bloom value, the faster they spread out. A lower Bloom value is better.

It is similar to recoil.

You want a low bloom for more accurate fire. Higher bloom results in less accurate shots.