Slackpacking is the art of traveling light during a hike while generally not sleeping outdoors, but at a hotel, hostel or at home. Often achieved by having support from friends who carry the bulk of your supplies by car or truck and meeting with you at staging points along the way or that take you back to your car. Also can mean diversionary short hikes with a light backpack, with supplies left behind at a basecamp.
Some Thru-hikers have been known to look down upon slackpackers as not being “pure”, which is why remembering to hike your own hike is important. Different strokes for different folks.