It should be noted that in the history of computer games 3D has stood for quite different things. Roberta Williams' original 1984 King's Quest for example was marketed as a 3D animated adventure since the display was layered: the hero sprite would move behind some of the decorations. More consistently it was used well into the 90s for what is nowadays known as the isometric view, mostly in the term 3D action adventure, a popular genre at the time.
The 3D games Beginnings
Some of the first 3D games were developed for the BBC, a platform that, like the PC, had decent computing power but no hardware sprites.