A ring- or donut-shaped area or structure. / (geometry) The region in a plane between two concentric circles of different radii.

(mycology) Describes an annulus with two layers of tissue.

(mycology) An annulus which is fixed to the stem of a mushroom and is not movable.

(mycology) Describes an annulus with just one layer of tissue.

(mycology) An annulus near the top of a mushroom’s stem

annulus fibrosus cordis / annulus fibrosus disci intervertebralis / annulus fibrosus tympani

(anatomy) A ring of fibrous tissue surrounding the optic nerve at its entrance at the apex of the orbit.

the region enclosed by two concentric squares with parallel sides

plural of annulus