The cricoid cartilage, or simply cricoid (from the Greek krikoeides meaning "ring-shaped"), is the only complete ring of cartilage

Cartilage

Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...

 around the trachea

Vertebrate trachea

In tetrapod anatomy the trachea, or windpipe, is a tube that connects the pharynx or larynx to the lungs, allowing the passage of air. It is lined with pseudostratified ciliated columnar epithelium cells with goblet cells that produce mucus...

.
The cricoid cartilage sits just inferior to the thyroid cartilage

Thyroid cartilage

The thyroid cartilage is the largest of the nine cartilages that make up the laryngeal skeleton, the cartilage structure in and around the trachea that contains the larynx....

 in the neck

Neck

The neck is the part of the body, on many terrestrial or secondarily aquatic vertebrates, that distinguishes the head from the torso or trunk. The adjective signifying "of the neck" is cervical .-Boner anatomy: The cervical spine:The cervical portion of the human spine comprises seven boney...

, and is joined to it medially by the median cricothyroid ligament

Cricothyroid ligament

The cricothyroid ligament is the larger part of the laryngeal membrane, continuing inferiorly as a median or anterior part and twin lateral ligaments....

 and postero-laterally by the cricothyroid joints. Inferior

Inferior

Inferior means of lower station, rank, degree, or grade . It may also refer to:* Inferiority complex* An anatomical term of location* Inferior angle of the scapula, in the human skeleton...

 to it are the rings of cartilage around the trachea (which are not continuous - rather they are C-shaped with a gap posteriorly).