what kind of movement is observed in the mimosa pudica plant when touched?

The movement observed in the Mimosa pudica plant when touched is a nastic movement , more specifically seismonastic (thigmonastic) movement caused by changes in turgor pressure in its cells.

In simple terms: when you touch the plant, its leaves quickly fold and droop due to a rapid loss of water (turgor) from special cells at the base of the leaf (pulvinus), making it collapse temporarily.