- In medicine, a membranous structure that envelops an organ, a joint, tumor, or any other part of the body. It is usually made up of dense collagen-containing connective tissue.
- In pharmacy, a solid dosage form in which the drug is enclosed in a hard or soft soluble container, usually of a form of gelatin.
- In microbiology, a coat around a microbe, such as a bacterium or fungus.
Derived from the diminutive of the Latin word "capsa" meaning "box", a capsule is literally "a little box" and can refer to any encompassing structure or small container.