An AT Hiker Glossary
The Appalachian Trail is marked with white blazes, with other colored blazes to mark side trails. There is a vernacular around other colored blazes ...
White-Blazer - An AT hiker who hikes the trail as defined by the white blazes that mark the trail proper - No deviations to skip unpopular sections, or to bypass a mountain summit.
Blue-Blazing - Taking alternate blue-blazed routes off the main trail. Often trails leading to a mountain summit have a blue blaze going around, rather than over, the summit to be taken in extreme weather. But more generically, it's taking any detour off the main trail and skipping white blazes.
Yellow-Blazing - Following those yellow blazes down the middle of a highway - In other words, hitchhiking to avoid sections of the trail, or to catch up with friends.
(Those last two are considered the most vile forms of cheating by many hikers.)
Aqua-blazing - Paddling down-river. Some AT hikers will rent kayaks in Waynesboro, VA, and paddle down the Shenandoah to Harper's Ferry, WV. Still not kosher in thru-hiking, but those that do so are not necessarily placed in the same circles of hell as Yellow and Blue blazers.
Pink-Blazing - Following an object of one's desire down the trail.
Green-Blazing - Following hikers with weed down the trail.
Slack-Packing - Hiking sections with only a day-pack. Often hostel operators will lend hikers day-packs, and shuttle them a day's hike up the trail, so that they can hike back to their pack ... The hiker pays for that service, then spends another night at the hostel. The next morning they are shuttled back up the trail. A money maker for hostels.
Flip-Flopping - An alternative thru-hike in which one hikes half the trail on one direction, and the other half in another direction. Most commonly, thru-hikers who get to Harper's Ferry at a pace that wouldn't allow them to get to the northern terminus in Maine before the trails up the mountain are closed, will flip to there, and hike back south to Harper's Ferry. Totally legit in all but the purest's eyes.
Purist - A fundamentalist white-blazer. One who absolutely does not skip any section of trail. Sometimes approaching obsessive/compulsive. I.e. There are places where one blue blazed trail leads in to a shelter area, and another leads out of it, causing one to miss maybe a tenth of a mile of the AT. A Purist always returns to the main trail on the blue blaze that they came in on. Many Purists also define their hike as carrying their full pack the whole way.