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"Coordinated" flight means an aircraft is in trim, that being a balance of forces including aerodynamic loads and power.

"Cross control" means the opposite, ie not in trim.

Trim is represented on the turn and slip indicator by the ball position as indicated in this image:



When the ball is centered between the two vertical wires the aircraft is in a trimmed state.

Cross control application is commonly used in fixed wing aircraft during landing in cross winds to align the aircraft with the runway on touchdown to avoid excessive lateral loads on the landing gear. Simply put, an aircraft is crabbing on final (flying cockeyed but trimmed) and then aligns by "slipping" or cross controlling. An aircraft is "cross controlled" when the rudder or in the case of helicopters, tail rotor control pedals, and ailerons/cyclic are deflected in opposite directions.

My reference to this in the previous chapters goes to the point that LOH pilots and gunners both typically sat on the same side and to provide the best view and field of fire, we typically flew sideways in various degrees depending on airspeed. Our operating speed while on missions ranged from a hover to 120 knots, but typically we were somewhere between 20 and 40 knots. 30-40 degrees of yaw to the axis of flight was fairly routine. It makes new guys puke fairly quick.