fantazija

1. imagination
   Deca imaju bujnu fantaziju. — Children have a vivid imagination.
2. fantasy; daydream
   To je samo tvoja fantazija, nije se desilo. — That's just your fantasy, it didn't happen.
   Plan da se obogatimo za godinu dana je čista fantazija. — The plan to get rich in a year is pure fantasy.
3. colloq. (approving) something amazing; a dream
   Torta je fantazija! — The cake is amazing!

The fantasy genre is usually called fantastika or epska fantastika in Serbian.