What is the meaning of unknown?

noun

• An unknown and unexplored region.
  • usage: "they came like angels out the unknown"
  • synonyms: unknown region, terra incognita
• Anyone who does not belong in the environment in which they are found.
  • synonyms: stranger, alien
• A variable whose values are solutions of an equation.
  • synonyms: unknown quantity

adjective

• Not known.
  • usage: "an unknown amount"; "an unknown island"; "an unknown writer"; "an unknown source"
• Being or having an unknown or unnamed source.
  • usage: "a poem by an unknown author"; "corporations responsible to nameless owners"; "an unnamed donor"
  • synonyms: nameless, unidentified, unnamed
• Not known to exist.
  • usage: "things obscurely felt surged up from unknown depths"
• Not famous or acclaimed.
  • usage: "an obscure family"; "unsung heroes of the war"
  • synonyms: obscure, unsung
• Not known before.
  • usage: "used many strange words"; "saw many strange faces in the crowd"; "don't let anyone unknown into the house"
  • synonyms: strange