A "microaggression" is a subtle, often unintentional comment or action that conveys bias or discrimination against a marginalized group. For example, asking a person of color, "How did you get this job?" telling a colleague with an accent, "Your English is so good," or scheduling team-building activities at bars, knowing some employees don't drink for religious reasons.
In the right circumstances, however, microaggressions can also amount to an adverse action that supports a workplace retaliation claim.
Consider the recent case of Uchitel v. Solid Waste Services.