Hiding is a game mechanic for the game Five Nights at Treasure Island: Found introduced in the remastered version. As revealed in AnArt's files, it was going to be in the original demo but a memory leak with Gamemaker prevents the source code that includes this to build.
Holding SHIFT allows the player to hide under the desk in The Office until a Suit leaves The Office. A message will appear at the bottom of the player's screen that explains to hold shift to hide. Hiding for too long will cause Slester to jumpscare you.