When rain water has soaked the ground to the point it can hold no more water, the ground is considered to be fully

Fully Saturated

Explanation:

Usually, a saturated solution refers to the condition where there is no more addition of solute to the solvent. This also can be considered to be the saturated point of the solution.

In the given condition, the rainwater is continuously soaked into the ground, and there comes a point when this water can no longer hold by the ground. As the ground reaches the saturated point, so it can be considered that the ground is in a fully saturated condition.