noun
blur; lack of focus; unsharpness
Refers to a blurred or out-of-focus state, especially in photography or vision.
この写真はボケがひどい。
This photo is badly blurred.
背景のボケがきれいなレンズだ。
This lens produces a beautiful background blur.
From the verb ぼける (to be blurred). The katakana spelling ボケ is common for this noun sense.