"Black Lives Matter" can refer to several aspects of a far-reaching social justice movement.
The Black Lives Matter organization (and its eponymous website and hashtag) began in 2013, after George Zimmerman was acquitted of shooting unarmed black teenager Trayvon Martin. The group was created by activists Patrisse Cullors, Opal Tometi, and Alicia Garza-- a contribution for which they often do not receive credit.
The organization's demands include the arrest of Darren Wilson (the officer who killed Michael Brown), a decrease in law enforcement spending and a reinvestment of that money into education, housing and jobs in majority black communities. A full list can be found on their website.
Why is this important?
The phrase "Black Lives Matter," has come to bind together the slogans of other flashpoints of police violence and racism over the last two years. Among them are "Hands Up, Don't Shoot," and "We Can't Breathe," in reference to the deaths of Michael Brown (2012) and Eric Garner (2014), respectively. Co-founder Opal Tometi emphasizes that the movement is not isolated to police violence, but rather includes all the ways black Americans are marginalized and brutalized. "Our lives are being systematically attacked all across the board... it is not just at the hands of the police," she states.
This is a national conversation that can't be ignored.
One more thing...
Some have countered the #BlackLivesMatter movement with #AllLivesMatter, promoting the idea that we should focus on everyone's experience equally.
#AllLivesMatter misses the point.
The cartoon below encompasses the mistake well: those who try to expand to #AllLivesMatter ignore the realities of racism and discrimination against black people in our country-- issues #BlackLivesMatter is moving to address.