noun
Refers to the spreading or blurring of ink, paint, or color beyond its intended area, often on paper or fabric.
この紙はにじみが少ないので、万年筆に向いている。
This paper has little bleeding, so it's suitable for fountain pens.
水彩
In watercolor painting, I use color bleeding as an expressive technique.
にじみ is the noun form of the verb にじむ (to blur, to bleed). にじみ refers to the result or phenomenon of bleeding, while にじむ describes the action.
Noun form of the verb にじむ (to blur, to run). The kanji 滲 is a non-Jōyō character meaning 'to seep' or 'to ooze', but the word is almost always written in kana.