Black Power is a pro-Black slogan, notably used by the Black Panther Party.
Leftist Wikipedia claims that it is also a name for a movement including a wide variety ideologies and organizations, including "Black nationalism", "Afrocentrism", "Black anarchism", "Black separatism", "Black feminism", "Pan-Africanism, and "Black leftism". That the individuals and organizations labeled by Wikipedia as being part of this movement themselves used or use the label may be dubious. Wikipedia is also very unclear with how to define it, giving various definitions, sometimes positive, sometimes contrasting it with the Civil Rights Movement as being different by supposedly advocating violence and Black supremacism.
The Black Power movement is stated to have been most prominent in the late 1960s and early 1970s.