Apparate

Apparating is the most advanced means of magical travel in the fictional Harry Potter series. All other means are either slower or require the use of magical objects. An apparating wizard or witch will disapparate (disappear) from one place and reappear in another almost instantaneously, effectively teleporting. Both apparating and disapparating are typically accompanied by a distinctive cracking sound, possibly caused by the abrupt motion of air due to the sudden presence or absence of a body.

Spoiler warning: Plot or ending details follow.

Apparating is tricky and an improper attempt can cause severe bodily damage, hopefully reversible by the Ministry of Magic's Accidental Magic Reversal Squad. As such, it's strictly restricted to adults and requires a license (issued by the Department of Magical Transport upon the passage of an Apparition Test) that's analogous to a driver's licence in the Muggle world. It is also considered unreliable over long distances, and even experienced users of the technique may prefer other means, like broomsticks.

The books may suggest that apparating also has something to do with the wizard or witch magically peeking at their desired new position before actually displacing themselves. In Harry Potter and the Order of the Phoenix, Fred and George Weasley apparate from one room to another to show off and end up sitting painfully on Ron's knee instead of the edge of his bed (they apologise by saying that it's harder in the dark).