noun (n)

• the concentration of your efforts on a particular field of study or occupation(noun.cognition)

  source: wordnet30
• the special line of work you have adopted as your career(noun.act)

  Synonym:
  specialisation, speciality, specialization, specialty
  

  source: wordnet30
• Devotion to a particular and restricted part or branch of knowledge, art, or science; as, medical specialism.(noun)

  source: webster1913