Purely a slogan.
Black lives taken by other blacks - a rate 10x that of whites murdered by whites - don't matter.
The half of black pregnancies ending in abortion don't matter.
And it isn't even police brutality that matters to them, because whites, hispanics and Asians killed by cops don't matter to them.
Their entire movement is demanding civil authorities give them money and power over their own communities and everyone else on the whole, regardless of the safety or rights of others. It is a power play akin to police no go zones in Europe where Muslim imams control everything to the point officials engage with the community by talking to the imams.