A trabecula (plural trabeculae, from Latin for "small beam.") is a small, often microscopic, tissue element in the form of a small beam, strut or rod, generally having a mechanical function, and usually composed of dense collagenous tissue (such as the trabecula of the spleen.) They can be composed of other materials; in the heart, for example, muscles such as trabeculae carneae and septomarginal trabecula form similar structures. The formation of trabecula is known as trabeculation.
On histological section, trabecula of a cancellous bone can look like a septum, but in three dimensions they are topologically distinct, with trabecula being roughly rod or pillar-shaped and septa being sheet-like.
When crossing fluid-filled spaces, trabecula may have the function of resisting tension (as in the penis, see for example trabeculae of corpora cavernosa and trabeculae of corpus spongiosum) or providing a cell filter (as in the trabecular meshwork of the eye.)
Multiple perforations in a septum may reduce it to a collection of trabecula, as happens to the walls of some of the pulmonary alveoli in emphysema.
Diminutive form of Latin trabs, which means a beam or bar. In the 19th century, the neologism trabeculum (with an assumed plural of trabecula) became popular, but is less etymologically correct. Trabeculum persists in some countries as a synonym for the trabecular meshwork of the eye, but this can be considered poor usage on the grounds of both etymology and descriptive accuracy.