Investopedia / Joules Garcia Degrees of freedom is a statistical term that defines how many units within a set can be selected without constraints. Degrees of freedom allow data points in a sample ...

That's a six-degrees-of-freedom game. They've enjoyed a small revival in recent years thanks to sleeper hits like Overload and Zerograve, but 6DOF shooters are still awaiting a major comeback.

The other, simpler and cheaper to build, spans six. And both shoot with "six degrees of freedom," moving forward and back, up and down, right and left, and across three other perpendicular axes.