The first obvious difference between 2D and 3D is that 2D utilizes only two axes: X and Y; whereas 3D has an additional Z-axis. To explain how this works from a games perspective, see the following diagram:

Generally speaking, the z-axis is used for depth and is utilized so that the player can explore an environment like they would in reality whether it is from a third person or first-person perspective camera. The z-axis allows the added third dimension to an environment. 2.5D games utilize the z-axis to provide a sense of depth because the game is still fixed to the x and y-axes.

In saying that, it is important to know the differences between 2D, 2.5D, and 3D games. While there are many different stories, quests, and adventures that games can take us on, these experiences, at least in terms of their appearance and design, will differ depending on what axis they are using—x, y, or z.  Before we start creating any game in this book, we'll just briefly go through some examples of 3D and various types of 2D style games. In this way, you will learn about the differences between the two and what types of experiences that they can afford.