Green strength with reference to plaster means
Two strength properties of gypsum are reported:

Wet strength (also known as green strength),.
Dry strength.

The wet strength is the strength that is determined when water in excess of that required for hydration of the hemihydrate remains in the test specimen. When such excess water is removed by drying, the strength obtained is the dry strength. The dry strength may be two or more times as high as the wet strength. Consequently, the distinction between the two is of considerable importance.
Phillips Science of Dental Materials ed 12 pg 188
Dry strength
Compressive strength
Strength of dental stone due to green colour
The wet strength