The term "model minority" refers to a minority population that is seemingly characterized by positive traits rather than negative ones. In layman's terms, you might hear someone call a model minority group something like, "the good ones," or say that they're "not like those other groups." In the United States, this is particularly true of Asian populations, and especially East Asians (Chinese, Japanese, Koreans, etc.). Asian-Americans are often stereotyped as being high-achieving, hard-working, sometimes hyper-intelligent, quiet and uncomplaining, and usually good in a very narrow range of fields including math and certain musical instruments.
On the one hand, this means that Asian-Americans don't have to deal with some of the very negative steretoypes that other populations, such as African-Americans, do. For example, Asian-American men don't tend to be seen as threatening the way that African-American men do, which means that they are more rarely victims of police brutality and other reactive crimes. Asian-Americans are encouraged by society to aim high and don't have to hear how "lazy" or "greedy" they are.
However, one challenge of being a model minority is that anyone that doesn't fit the fairly narrow set of stereotypes associated with it tends to be treated as alien. Jeremy Lin is an excellent example of this in that Asian-American men are typically not seen as being good at sports. When he began playing basketball, he was extremely Othered in the media and by both white and Asian viewers for not being the way he "should" be. "Linsanity," his extremely vocal fanbase, primarily began because no one could believe that an Asian-American was as good at basketball as he is. By exclaiming over his abilities while constantly referencing his ethnicity, the media continued to highlight the fact that Asian-Americans are not expected to do well in that area.
One way this can be remedied is by simply acknowledging that stereotypes are stereotypes and that it should not be remarkable that an Asian-American man is good at sports, just as it should not be remarkable that an African-American man is a CEO or scholar. If the media focused on Jeremy Lin's achievements without making hay over his ethnicity, they would not have contributed to the stereotype.