- a tiny sphere or bead, often hollow or filled with some other substance: used for a variety of purposes, such as in building materials, cosmetics, and scientific research.
- Medicine/Medical.
- a tiny hollow sphere injected into a blood vessel in order to block the flow of blood to a tumor and, in some cases, deliver chemicals or radiation to kill the tumor’s cells.
- a tiny hollow sphere that can be injected into the bloodstream or, sometimes, implanted into a tissue of the body: used therapeutically to deliver medicine or nutrients, or diagnostically to study the flow of blood to a certain area.
