This designates the minimum pressure after the application that is absolutely essential to make a connection between the adherends possible at all.
The parts to be bonded must be joined together within the open time of the hot melt adhesive, whereby a low contact pressure is generally sufficient to allow the hot melt adhesive to wet the second substrate.
Pressure on the adherends must be just high enough to fix them in place during setting, in order that they cannot move against each other.
Schematic structure of a bond
Source: IVK, Die Kunst des Klebens, Abb. 1