The Nikko Rull brush is primarily known as a staple , located within the "Painting" set. While it is not a native Adobe Photoshop brush, it is highly sought after by Photoshop users for its unique textured, "roller-like" quality that mimics traditional media like linocuts or oil pastels. The Nikko Rull Brush: Characteristics and Usage
I guess it's just an alternative term for "roll" because all of his rull brushes are textured brushes that rezemble paint rollers. Painting a Landscape with the Nikko Rull brush in Procreate nikko rull brush for photoshop