The term typically refers to a style that is more laid back and relaxed when compared to regular and contemporary rock in order to make it more "authentic" when compared to other rock.
[1] Slacker rock is closely related to "slacker" culture that arose in the 1980s and 1990s with Generation X and can be seen in the way the music is composed with less emphasis on playing certain notes correctly, having slightly out of tune instruments, and having lyrics be sung in a form that was more relaxed similar to the slacker style.
[3] Taking influence from 1980s lo-fi bands like Beat Happening and Tall Dwarfs, slacker rock was pioneered by indie rock acts including Sebadoh, Pavement, Sparklehorse, The Apples In Stereo and Guided By Voices.
[4] The genre saw its height in the 1990s with popular artists like Beck.
[5] Since the 2010s, it has seen a revival with the likes of Mac DeMarco, Alex G and Courtney Barnett.