Rotor and mechanical turbulence are close cousins. Rotor is the rotational swirl that forms downwind of certain shapes, usually a persistent, strong rotational flow. Mechanical turbulence is a more random stirring of the air downwind of obstructions.
The distinction is of little use for us because we don’t typically fly near hills but, knowing the difference can be helpful since the shape of obstructions is important. Those that lend themselves to rotor are particularly dangerous since they can leave a fairly steady wind that’s lulls a pilot into launching into what is actually a rotor.
Watch this video to get an idea of how bad that can go. This is a good tool to help visualize what the air may be doing and hopefully to beg off conditions that would be rib-cracking or worse.
If you fly in mountainous areas there are plenty of videos that hit home, especially if you’re visiting the area and aren’t familiar with local idiosyncrasies. There’s no amount of skill that can prepare a pilot for the worst of what mother nature can dole out. Like the cyber-villain in “War Games,” who said after nuclear holocaust was barely averted: “the only good move is not to play.”