Just to clear some things up.
All the eroge game systems:
ADV: Where you play the role of a character and make decisions based mainly on dialogue. (Endings are usually decided by a tree decision route)
AVG: Where you play the role of a character where you make decisions where to go and/or who to talk to. (Endings are usually decided by which character you meet the most)
NOV(or NVL): Visual novels, where you mainly read text with a background picture. There is also choose your own adventure choices, but not always.
SLG: A broad term ment for strategy and/or simulation games.
RPG: I don’t have to explain this one. Fighting, leveling etc.
Others: Games that don’t follow into those genres are usually fan discs, mahjong games, arcade style games, etc
Sometimes, games actually have a hybrid game systems where they blend ADV with other genre such as SLG.
There is also the fact that even Japanese people and companies sometimes get confused as to what genre a game falls into and label them wrong. (AVGs marked as ADV (or vice versa))