The keeping of a thing from harm by something standing between. Protection implies a protector and a threat.
Latin protectio (a covering, a shielding), from protegere: pro- (in front) + tegere (to cover); protection names the covering itself, and it requires both a threat and something willing to stand in front of it.
The keeping of a thing from harm by something interposed between them. The root's cover is not passive — it has to be held there, which is why protection implies an ongoing protector rather than a one-time act.