“BIPOC stands for Black, Indigenous, and People of Color.
Black refers to dark-skinned people, especially of African, Caribbean, and Australian Aboriginal origin who were enslaved by white people.

Indigenous, here, refers to ethnic groups native to the Americas, and who were killed en masse by white people. People of color is an umbrella term for non-white people, especially as they face racism and discrimination in a white dominant culture.
Growing in use and awareness during the 2020 George Floyd protests against racism and police brutality, BIPOC is meant to emphasize the particular hardships faced by Black and Indigenous people in the US and Canada—especially because Indigenous people often get forgotten in social justice causes and that anti-Black racism is particularly virulent.