I've never heard that term either, but it would technically make sense if it's the literal opposite of hypertrophy, so yeah, I'd figure it's essentially the same as atrophy.
Can you flex the muscles on the right side, without weights, like you can the left? Just wondering. It's of course not uncommon to have one side stronger and/or bigger than the other, but it'll certainly be more noticeable since you have legit underlying issues. I'd also be sure to address whatever you can with tissue quality work (foam rolling, mobility work, stretching of all sorts), in addition to whatever weight room changes you're doing.