Introvert

 A person who prefers calm environments, limits social engagements, or embraces a greater than average preference for solitude. 

• PSYCHOLOGY

  a person predominantly concerned with their own thoughts and feelings rather than with external things.

  "introverts seek out and enjoy opportunities for reflection and solitude"

a person whose personality is characterized by introversion : a typically reserved or quiet person who tends to be introspective and enjoys spending time alone. Note: Introverts are typically more comfortable interacting with small groups of people rather than large groups