introversion

Short definition from Wiktionary

Noun

1. 1
   A turning inward, particularly
2. 2
   A turning inward: The action of turning one's thoughts upon internal or spiritual matters.
3. 3
   A turning inward: A personality orientation towards the self and mental abstraction; behavior expressing such orientation.
4. 4
   A turning inward: Arrangement of two similar words, lines, etc. to form the middle part of a structure.