Margins:

Mark all available items or objects as selected.

Mask ID:

Mask from opacity

Matches pixels with similar alpha value (opacity/transparency).

Matches pixels with similar brightness.

Matches pixels with similar hues.

Matches pixels with similar values in red, green, blue and alpha channels.

Matching files:

Maximize contrast of each of the red, green, and blue color channels.

Maximum Colors

Maximum color value. Recommended values are 1 (the native HDR range), 100 (percent range), or 255 (classic 8-bit color).

Maximum difference between the color of the clicked pixel and the color of the flood-filled pixel. Values range from 0 to 100%.

Maximum distance in pixels that each pixel is influences.

Maximum energy of a pixel to consider it noise.

Mean removal

Media

Menu configuration

Merge layers

Merged