What is the meaning of classified?

noun

• A short ad in a newspaper or magazine (usually in small print) and appearing along with other ads of the same type.
  • synonyms: classified ad, classified advertisement

verb

• Arrange or order by classes or categories.
  • usage: "How would you classify these pottery shards-are they prehistoric"
  • synonyms: classify, class, sort, assort, sort out, separate
• Declare unavailable, as for security reasons.
  • usage: "Classify these documents"
  • synonyms: classify
• Assign to a class or kind.
  • usage: "How should algae be classified"; "People argue about how to relegate certain mushrooms"
  • synonyms: relegate, classify

adjective

• Arranged into classes.
• Official classification of information or documents; withheld from general circulation.
  • usage: "thousands of classified documents have now been declassified"