any foreign matter, as a blood clot or air bubble, carried in the bloodstream and capable of causing an embolism
See embolus in American Heritage Dictionary 4
(ĕmˈbə-ləs)
nounpl.em·bo·li(-līˌ)
A mass, such as an air bubble, a detached blood clot, or a foreign body, that travels through the bloodstream and lodges so as to obstruct or occlude a blood vessel.