English

Noun

1. A ring- or donut-shaped area or structure.
2. In mathematics, the region between two concentric circles of different radius.
3. In astronomy, the ring of the sun not covered by the moon in an annular solar eclipse.
4. The membranous remnants of a partial veil which leaves a ring on the stem of a mushroom.

• Annulus (entomology), an antennal unit in simple antennae, or a ring-like marking or structure surrounding a joint or segment.
• Annulus (Herpetology), reference to too small an opening that can be a potential death trap for a reptile that can't pass through. The size difference of the two cylindrical forms (The body of the animal vs. the circumference of the opening).
• Annulus (geology), the opening between an outer and inner cylindrical body, often used to describe the space between the well screen or drill pipe and the surface of the bore hole.
• Annulus (anatomy) refers to several structures in human anatomy. The spelling "anulus" is preferred under Terminologia Anatomica, but both spellings are commonly found. Examples include:
  • Annulus fibrosus cordis, the ring-like structure on a heart valve where the valve leaflets are anchored
  • Annulus fibrosus disci intervertebralis, the outer wall of the invertebral disc
  • Annulus femoralis
  • Annulus inguinalis superficialis
  • Annulus inguinalis profundus
  • Annulus tendineus communis
• Annulus (ichthyology), the annual rings that form in fish scales or bone sections
• Annulus (mycology), the "ring" on a mushroom stem
• Annulus (astronomy), the ring of light from the visible part of the photosphere seen at the greatest extent of an annular eclipse
• Annulus (cosmology), the ring around the lens on which strong gravitationally lensed images of one source appear
• Annulus (mathematics), a ring-shaped geometric figure
• Annulus (firestop), the space in a penetration seal surrounding a penetrant, i.e. between a pipe or electrical conduit, or cable and a sleeve, with or without a firestop
• Annulus (oil well), the tube shaped void between a pipe string and a surrounding pipe string or formation.
• Annulus (microscopy), a circular opening "disk" below a specimen slide, required for Phase Contrast microscopy

• Annular hurricane, a hurricane that is nearly symmetrical and takes longer to weaken than normal hurricanes.

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