Japanese adult dating game
There are many variations on this theme: high-school romances are the most common, but a dating sim may also take place in a fantasy setting and involve such challenges as defending one's girl from monsters.
One game series that often includes dating, with the goal of marriage, is the farming sim series Harvest Moon.
Sexually explicit dating sims may fall into the category of H Game or Eroge.
Eroge only gets released to PC because large Japanese game companies do not want to release games with sexual content on their game consoles.
When the game ends, the player either loses the game if he failed to properly win over any of the girls, or "finishes" one of the girls, often by having sex with her, marrying her (as in Magical Date), and/or achieving eternal love.
Homosexual relationships are also possible, as there are games with no specific gender lines ("all pairings").
There are also Girls' Love games, which focus on female/female relationships, and Boys' Love games, which focus on male/male pairings.
This group may include any game with significant amounts of nudity and/or explicit sex scenes that was either made in Japan or clearly imitates the Japanese way of making such games.
Hentai (Japanese 変態, "perverse"; can also be understood as "shape-changing" or "weirdly shaped") is the term commonly used in the West for such games.