What you have marked with the arrow means that the PseudoTransient under relaxation technique is only available when you are using the steady-state solver. If you were using the transient solver this option will not be available (because it is a true transient simulation and therefore cannot be “pseudo”).

If you have defined a steady-state solution, then you are running a steady-state simulation. Unticking this box just changes how the solver operates behind the scenes.

EDIT: Why do I always have to edit to get the formating right on these posts? Arrrggg!