"Economic migration" is a (usually derogatory) term for moving into a country to earn more money, with no desire to adapt to the culture of your new home.
Often times the children of such migrants adapt pretty well. I think the term is more euphemistic and neutral than derogatory. It's more like a category that's existed for centuries (but gets more stigma now) because some the older generations who have been in the U.S. for a few decades now look down on those "fresh off the boat," the same way those before them did to them. Irish fled the Potato Famine in the 1850s- they were economic migrants too.
I never really thought of it as a subset of immigrants who move to get rich but not adapt. Lisa Su, Satya Nadella, Sundar Pichai and Jensen Huang are also economic migrants. Just because they adapted/assimilated more than others doesn't make them _not_ economic migrants.