You can find this filter through Filters → Generic → Erode

This filter widens and enhances bright areas of the active layer or selection.

For every image pixel, it brings the pixel Value (luminosity) into line with the upper Value (the brightest) of the 8 neighbouring pixels (3x3 matrix). So, a bright pixel is added around bright areas. An isolated pixel on a brighter background will be deleted. A larger bright area will dilate by one pixel in all directions.

On complex images, bright areas are widened and enhanced the same, and somewhat pixellated.

On a solid background, this filter can delete noise: