Chuunibyou demo Koi ga Shitai! Wiki
The main characters in the story are chunibyo, a mocking term for immature behavior of young teenagers in which they act out grand delusions, or pretend that they have magical powers such as those of anime characters. Chūnibyō (sometimes spelled 'chuunibyou'), is literally translated as "middle 2 syndrome" (middle [school] second [year] syndrome), which also goes by the short form 'chu2', and is often translated to English as "eighth-grader syndrome".

The term was created by talk-radio host Hikaru Ijuin in 1999, referring to childish behaviour in youngsters who were expected to have progressed beyond such make-believe. His intention was somewhat affectionate, as if such people were remaining young at heart.  By 10 years later, the term had become so evolved and different from his initial concept, that he disavowed himself from the word, due to the derogatory nature that it had turned into, allowing any harmful affects on the person to be dismissed as the fault of their own affliction. 

"Someone that allows daydreams, fantasies, and exaggerated unrealistic self-identification to become so compulsive and consuming that the behavior affects and obstructs positive social interactions and hinders productive maturation, or even places the individual in potentially harmful circumstances, suffers from chuunibyou" - John Oppliger (Ask John) of AnimeNation

While the flights of fancy imagined by Rikka, Shinchumiya, and Dekomori in the Love, Chunibyo, and Other Delusions series are largely harmless to them, other manga and anime characters with similar dreamlands are not so lucky.  For example, Ichiro of the Aura: Koga Maryuin's Last War series was bullied throughout middle school, and then is assigned to help a similar individual who has been subjected to such ridicule.