An overview of illustrations and explanations of different types of gills, which are extremely helpful for identifying mushroom species.
Illustrations taken from Wikipedia user Debivort with license: CC-BY-3.0.
The gills do not have contact with the stem
The gills have some contact to the stem
The discs have wide contact with the stem, whilst also growing at a similar angle to the stem.
The gills clearly grow down along the stem.
The gills are attached downwards along the stem, but only slightly. N.b this is not always visible.
The gills recess along the stem.
alt. Recessed with notches
Gill are recessed at the innermost part of the stem, but also a descent into notches along the stem.
The gills are well established in young fungi, but in older specimins the edges will break away. You can sometimes see remnants of this still attached to the stem.