Heroic items are the ones that come color coded in dark red. You won't come across these until very late in the storyline at the earliest. I found my first Heroic in Act 4, at level 45, on Very Hard difficulty. The higher the difficulty, the more likely you are to come across one of these items. They're more apt to drop from killing an Elite or one of the Grand Chests (the bigger chests you can find while exploring the map, not the smaller ones).