The Lingered is a collective term used to refer to the ghosts and demons that are encountered in the school.
Types of Lingered
There are 3 types of lingered encountered, the basic Lingered, the Lantern Specter, and an unnamed larger creature with many arms.
The basic lingered is first encountered near the beginning of Chapter 1, and wander around areas of the school with no clear purpose. They appear as silhouettes of girls, with a mouth that hangs open and a spine that bends backwards when they run. They emit a mixture of crackling, breathing, crying, and laughing sounds when nearby. They can be baited with food offerings, and appear to be capable of short-range teleportation.
The lingered can be found wandering around or eating. Approaching one will cause it to attack and chase the player, although they will lose interest quickly if the player runs away. In order to get past them, the character must hold their breath (right mouse button to toggle) and walk past them. The character can only hold their breath for about 15 seconds, so it may be helpful when the first lingered is encountered to practice how close you can get without holding breath before it attacks. Lingered who are moving in the same direction as you are difficult to pass, so you should wait for them to turn around.
They can also be distracted with a food offering. The nurses office in Chapter 1 provides a regenerating supply of them. When used, the food item will be placed at the character's feet, and any nearby lingered will run towards it and begin eating it, a process which lasts about 25 seconds.
The character can survive 3 hits in rapid succession from a normal Lingered, with the 4th hit killing them.
Lantern Specters or Lantern Spirits are about twice as tall as the character, with short tentacle-like appendages on their face, wearing a green or blue coat and holding a lantern out in front of them. Like the normal lingered, they wander around, but can not be seen or heard from a distance. They appear when the player is about half a screen-length from their location, and are often announced by Ray gasping shortly before they fade into view.
Lantern specters are a little more complicated to deal with than normal lingered, but easier to consistently pass. When it approaches, face away from it and hold your breath until it passes. You can actually get pretty close to it without needing to do either of these things - you don't need to turn around until the character is about even with the lantern, and you don't need to hold your breath until the spirit starts to bring its head down to look at you. Once it continues walking, you can release your breath and move on once the character is about even with its legs.
Getting caught by the lantern specter results in instant death.
The third, unnamed lingered appears at only a few points in the game, and always in a cutscene fashion. It appears to be a silhouetted and slightly transparent mass of human arms atop a pair of human legs.