What is the meaning of sphere?

noun

• A particular environment or walk of life.
  • usage: "his social sphere is limited"; "it was a closed area of employment"; "he's out of my orbit"
  • synonyms: domain, area, orbit, field, arena
• Any spherically shaped artifact.
• The geographical area in which one nation is very influential.
  • synonyms: sphere of influence
• A particular aspect of life or activity.
  • usage: "he was helpless in an important sector of his life"
  • synonyms: sector
• A solid figure bounded by a spherical surface (including the space it encloses. )
• A three-dimensional closed surface such that every point on the surface is equidistant from the center.
• The apparent surface of the imaginary sphere on which celestial bodies appear to be projected.
  • synonyms: celestial sphere, empyrean, firmament, heavens, vault of heaven, welkin