annulus

IPA: ˈænjʌɫʌs

A ring- or donut-shaped area or structure.
(anatomy) A ring of fibrous tissue; specifically (cardiology), such a ring around an opening of a heart valve, to which the valve leaflets and muscle fibres of the atria and ventricles are attached; an annulus fibrosus cordis.
(astronomy) A ring of light in a celestial body, especially when caused by an annular eclipse (for example, when the Sun and Moon are in line with the Earth, but the Moon does not completely cover the Sun's disc).
(biology)
(botany) A structure surrounding a sporangium (or part of it) which shrinks and causes it to rupture for spore dispersal; specifically, in a fern: a structure around about two-thirds of the sporangium consisting of differentially thick-walled cells which dry and distort the sporangium; and in a moss: a complete ring of cells around the tip of the sporangium which dissolves to cause the tip to detach.
(mycology) The membranous remnants of a partial veil which leaves a ring on the stem of a mushroom.
(mathematics)
(geometry) The region in a plane between two concentric circles of different radii.
(topology) Any topological space homeomorphic to the region in a plane between two concentric circles of different radii.
(technology) In a well such as an oil well or water well: the space between a pipe or tube and any pipe, tube, casing, or sides of a hole surrounding it.

Examples of "annulus" in Sentences

One of the biggest variables is whether the area called the annulus, which is between the inner piping and the outer casing, has sprung an oil leak.
No one is sure if the oil and gas are flowing inside the pipe or outside the casing in what is called the annulus -- the space between the pipe and the rock wall of the hole.
One of the biggest variables on the static kill's finality is whether the area called the annulus, which is between the inner piping and the outer casing, has sprung an oil leak.
U.S. officials are concerned that the flooding of that area, known as the annulus, could compromise a cement plug that the company installed in early August at the top of the well.
BP Senior Vice President Kent Wells said it's "really a possibility" that cement that engineers pumped in through the top went down into the reservoir, came back up and plugged the annulus, which is between the inner piping and the outer casing.
U.S. officials were concerned that the injection of liquid into the gap between the well and the rock known as the annulus could compromise a cement plug that BP cast at the top of the well in early August, letting some oil escape into the ocean.
There is one scenario, not considered likely, in which hydrocarbons would be lurking in the space known as the annulus, between the casing and the rock wall of the well bore, said retired Coast Guard Adm. Thad Allen, the national incident commander.