(countable) A single elongated piece of a given material, roughly round in cross-section, often twisted with other fibers to form thread.

(uncountable) A material in the form of fibers.

(textiles) A material whose length is at least 1000 times its width.

Dietary fiber.

(figurative) Moral strength and resolve.

(mathematics) The preimage of a given point in the range of a map.

(category theory) The pullback of a morphism along a global element (called the fiber of the morphism over the global element).

(computing) A kind of lightweight thread of execution.

(cytology) A long tubular cell found in bodily tissue.