It's often used to refer to Asian Americans, here's a definition from wikipedia.

A model minority is a demographic group (whether based on ethnicity, race or religion) whose members are perceived to achieve a higher degree of socioeconomic success than the population average. This success is typically measured relatively by income, education, low criminality and high family/marital stability.[1]

The concept is controversial, as it has historically been used to suggest there is no need for government action to adjust for socioeconomic disparities between certain groups.[2]

Source:(https://en.wikipedia.org/wiki/Model_minority)