A genre of Love Comedy anime series, usually a bishoujo series. The charcters and designs have many similarities with harem anime, with some exceptions. One interesting observation is most male leads in Magical Girlfriend series are older than in typical harem anime.
A singular female lead with a strong or striking personality who is intended from Square One to be the lead's romantic counterpart. She has some unusual and theoretically useful abilities, although they simply need to be unique and not strictly magic. (An android, a fairy, or angel could all be considered Magical Girlfriends) Because of her alienness (sometimes literally) she often doesn't have preconceptions about people.
A lead male usually in his LATE teens or older, often college age. He is usually somewhat well-adjusted and often very devoted to the lead character.
Secondary characters who either provide 'lessons' in normalcy to the lead female and social tips to the lead male. They are not usually serious rivals for either's affections.
While harem anime rivals are usually other characters, in M.G. anime it's usually bad luck, circumstances, or fate that cause issues with the relationship's progression.
Happy World features a twist on the concept: A jaded, bitter, but fundamentally decent young man who sometimes treats his helpful but bumbling guardian angel like a annoying little sister.