noun (n)

• an operation that segregates items into groups according to a specified criterion(noun.process)

  Example:
  The bottleneck in mail delivery is the process of sorting.
  

  Synonym:
  sort
  

  source: wordnet30
• the basic cognitive process of arranging into classes or categories(noun.cognition)

  Synonym:
  categorisation, categorization, classification
  

  source: wordnet30
• grouping by class or kind or size(noun.act)

  source: wordnet30