Noun, smooth muscles
1. An involuntary non-striated muscle. It is divided into two sub-groups; the single-unit (unitary) and multiunit smooth muscle. They are found within the walls of blood vessels (such smooth muscle specifically being termed vascular smooth muscle) such as in the tunica media layer of large (aorta) and small arteries, arterioles and veins. Smooth muscle is also found in lymphatic vessels, the urinary bladder, uterus (termed uterine smooth muscle), male and female reproductive tracts, gastrointestinal tract, respiratory tract, arrector pili of skin, the ciliary muscle, and iris of the eye. The structure and function is basically the same in smooth muscle cells in different organs, but the inducing stimuli differ substantially, in order to perform individual effects in the body at individual times. In addition, the glomeruli of the kidneys contain smooth muscle-like cells called mesangial cells. (wikipedia.org)
2. Involuntary muscle which is found within the intestines, throat, uterus, and blood vessel walls. (wiktionary.org)
3. Muscle tissue in which the contractile fibrils are not highly ordered, occurring in the gut and other internal organs and not under voluntary control. (Google Dictionary)
4. A muscle that contracts without conscious control and found in walls of internal organs such as stomach and intestine and bladder and blood vessels (excluding the heart). (wordnetweb.princeton.edu)
5. Muscle tissue that does not appear striated under the microscope; has the form of thin layers or sheets. (wordnetweb.princeton.edu)
6. Muscle tissue in vertebrates made up from long tapering cells that may be anything from 20-500m long. (biology-online.org)