A slacker is someone who can't be relied on to do a job or finish a project. If you're looking for the slacker in your family, you'll probably find him on the couch.
Nobody wants a slacker on their soccer team. Slackers avoid effort of any kind, putting work off or getting someone else to do it for them. While slacker is commonly thought of as a word from the 1990s — there was even a movie called Slackers made in 1991 — it's actually been around since at least the late 1800s. In the early 20th century, Sudanese workers protested their lack of voice and power by slacking, or working very slowly.