Harry Potter and the Sorcerer’s stone

There were a hundred and forty-two staircases at Hogwarts: wide, sweeping ones; narrow, rickety ones; some that led somewhere different on a Friday; some with a vanishing step halfway up that you had to remember to jump. Then there were doors that wouldn't open unless you asked politely, or tickled them in exactly the right place, and doors that weren't really doors at all, but solid walls just pretending. It was also very hard to remember where anything was, because it all seemed to move around a lot. The people in the portraits kept going to visit each other, and Harry was sure the coats of armor could walk.

The ghosts didn't help, either. It was always a nasty shock when one of them glided suddenly through a door you were trying to open. Nearly Headless Nick was always happy to point new Gryffindors in the right direction, but Peeves the Poltergeist was worth two locked doors and a trick staircase if you met him when you were late for class. He would drop wastepaper baskets on your head, pull rugs from under your feet, pelt you with bits of chalk, or sneak up behind you, invisible, grab your nose, and screech, "GOT YOUR CONK!"

Source: Harry Potter book

 19. What does glided in the text above mean?