A groove, furrow, or trench. The plural is sulci. In anatomy, there are many sulci; an example is the superior pulmonary sulcus.

A fissure or groove

(sulci = pl.), a groove, trench or furrow; in neuroanatomy, for instance, a depression or groove on the brain surface separating the gyri.

plural sulci, "fissure between convolutions of the brain," 1833, from medical use of Latin sulcus "furrow, trench, ditch, wrinkle," apparently literally "the result of plowing [..]

the valleys or spaces between the folds or gyri of the brain (Sheep Brain Dissection)

A furrow in the pollen surface of a non-eudicot plant. (Plural, sulci)

(sul´kus) A shallow impression or groove. superficial

It is one surface of the cerebral cortex.

A furrow of a convoluted brain surface. See Figure 2.12. Compare gyrus.

(n) (anatomy) any of the narrow grooves in an organ or tissue especially those that mark the convolutions on the surface of the brain

Upper eyelid depression.

Sulcus (singular sulci) are the “dips” on the brain surface.

A broad groove; on the brain’s surface the sulci are the valleys between the gyri.

A suture which is deeply grooved or forms a distinct furrow.

A groove or furrow, as one of the grooves on the surface of the cerebrum in mammals.

(anatomy) A furrow or groove in an organ or a tissue. (anatomy) Any of the grooves that mark the convolutions of the surface of the brain. * '''1999''', Thomas C. Pritchard, Kevin D. Alloway, ''M [..]