Five Nights at Freddy's (often abbreviated as FNaF) is both the name of a point-and-click video game developed by Scott Cawthon, released in August 8th, 2014, and also the subsequent series after the initial game. Set in a location known as Freddy Fazbear's Pizza, the first survival horror game puts the player in the shoes of a rookie security guard doing the graveyard shift at a children's entertainment center. Four animatronic entertainers free-roam at night with malign intent. If they succeed in reaching the player in his office, he will be forced into the sharp insides of an animal suit and killed.

The protagonist must manage power usage carefully while watching the cameras, triggering the doors at the right time in order to prevent the four (Bonnie, Chica, Foxy, and leader Freddy Fazbear) from entering the office. Making it to 6am wins that night and completes a section of the game. If the power runs out, however, Freddy quickly makes it to the guard, playing a macabre song, and murders the player.

The animatronics are haunted by the spirits of five children that died years ago at the hands of a psychotic killer (known as the Purple Guy) who had worn a Freddy costume. Though it's stated in game that the animatronics merely wish to stuff the player inside a suit because they think that they are simply helping out a friend without a costume, fans generally think that the animatronics are out for revenge. It's heavily implied that the murderer was a former guard who eventually perishes himself (as seen in Five Nights at Freddy's 3), although many details about the multi-game story-line remain uncertain.

On August 24th, 2020, Scott Cawthon announced the Fazbear Fanverse Initiative, a collaboration between him and 5 fangame developers to profit their games and sell them as if they were official FNaF games. The initiative consists of 4 fangame series and an official remake/reimagining of the first game.

For more information:

Five Nights At Freddy's (Wikipedia)