RPG = Role Playing Game
You play a role, and act as the character would in each situation.
In other words, D&D.
The acronym was borrowed to refer to almost any game that had turn-based battles, level-building, or just contained 'dungeons' and 'dragons'.
Zelda games don't even allow choice, and Link is almost devoid of character. It would be most accurate to refer to the series as "Adventure" games.