Lolicon or Lolita Complex is the attraction or fixation towards little girls. The Japanese definition doesn't make a distinction between fictional and real little girls (although some people will clarify their preference for 2D), but outside of Japan the term is commonly used within otaku circles for the sexual attraction towards loli characters and for the hentai genre featuring them.
If you need more information, I would recommend you to look up the books of Patrick Galbraith, and this video which is part of a series featuring him:
https://youtu.be/lETPaGnl2aI 