Poofing is a phrase coined by Edilio (although first used by Quinn who described their history teacher's disappearance in the first few pages of Gone), describing the occurrence of someone reaching the age of fifteen or above and disappearing, tempted out of the FAYZ by the Gaiaphage, which was presumed to devour them and assimilate their intelligence and powers. As a teenager Poofs, they see those they love telling them to follow them. If the poofer refuses, their loved-one morphs into something evil and threatens them. Many teens refused this monster and avoided Poofing, due to fear over what happens after Poofing. Astrid wrote a book, when printers were still available, explaining how to survive the poof but it soon became overlooked.
Some teenagers who "Poofed" were later discovered outside of the FAYZ, such as a pair of twins, Emma and Anna, were unharmed when they Poofed. Some later Poofers, including Mary Terrafino and Francis were not so lucky. Exactly what happens during Poofing is unknown. The Poof is also called the Big One-Five and has also been called "stepping out" of the FAYZ.
Poof was when anyone disappeared. Anyone over the age of 15 disappeared. Those who turned 15 had a choice. No one knows what's going to happen. This "poofing" crisis was caused by Little Pete who got mad at the adults for being loud and removed everyone the age of 15 or older. Those who turned 15 had a choice though somehow.