A colloquial phrase used primarily in Spain that translates to 'in his/her daydream'. It's used to describe someone who is lost in their thoughts or daydreaming, not paying attention to the surrounding reality.
Examples
- Spanish: Juan está en su alucin, no se ha dado cuenta de que hemos cambiado de tema.
- English: Juan is in his daydream, he hasn't realized that we've changed the topic.