Microaggressions are defined as the everyday, subtle, intentional — and often unintentional — interactions or behaviours that communicate bias toward historically marginalized groups.
The difference between microaggressions and overt discrimination, or macroaggressions, is that people who commit microaggressions are often not aware of them; but this does not mean that their impact is not incredibly harmful. You can learn more about this important issue through this short video. It is really well done and worth watching.