Can somebody explain?
I'm no expert but surely that would be 'contact' force as it is the fact of B contacting A that is causing the deformation. If on the other hand it was the same scenario but B resulted with a deformation then I would assume that it would the be 'reaction' force.
This is purely guess work, but seems logical to me!
Let me add the following :
Reaction forces can be used to display forces on a restrained surface due to external loading. Whereas contact forces can be shown in contact areas (e.g. between two components).
Check out these guys :
2018 SOLIDWORKS Help - List Contact/Friction Force
Thanks for your explanation! I also realized you can only analyze the reaction force on a fixed / externally restrained surface. Initially i though the reaction force would be the force from my part exerting on earth. But in Solidworks this feature seems to be purely to analyze fixture forces. Mistery solved!