HOTAS as an acronym stands for "Hands On Throttle And Stick", basicly describing a joystick that can be connected to a PC or a console in order to deliver a maximum in realism, immersion and
flexibility to the user.
What sets a HOTAS apart from an "average joystick" is that is consists of two modules that are in some way
physically connected:
The "stick" and the "throttle".
Each requires the use of one hand for
operation, hence the name.
The only ways of further upgrading a HOTAS system are adding control pedals and/or a head-mounted motion-tracking system.
If you're serious about flight-sims, you won't get around
purchasing a HOTAS.
To date the most complete and
critically acclaimed models are for a
realistic(flight-sim) approach Thrustmaster's Cougar HOTAS and for a sci-fi(MechWarrior/Space-sim) approach Saitek's X52.