An irritating-yet-innocuous type of trap in NetHack. If you step on one of these, it squeaks loudly and awakens/attracts nearby monsters. In a lot of ways, this is probably by far the least of your worries in the untimely-demise-fraught Dungeons of Doom, where some hapless Wizard or Barbarian is no doubt having their brains devoured by a mind flayer as you read this.

Squeaky boards can be desqueakified by the thorough application of a potion of oil, or a few dabs out of the mysterious can of grease. I'm assuming it's mumak grease, because there aren't too many other NetHack creatures I can see being boiled down and rendered.