Prop Hunt is a game of hide n seek in which a team of players can disguise themselves in different in-game objects (props) and the other team of human players (Hunters) have to find them out. The prop team has a new weapon at their disposal "Prop-O-Matic" which transforms them intro props. The goal of the prop theam is to evade and survive the Hunters.

Fortnite - Prop Hunt

About the mode (from the website):

Prop Hunt! The classic community mod has been reimagined within Fortnite by the talented StrayKite dev team. Faceoff in a thrilling game of hide and seek with a twist. Hiders can turn themselves into almost any decorative object (prop) on the map. Their objective, to evade the Hunters and survive until time runs out. The Hunters are tasked with finding and eliminating all of the Hiders within the time limit.

The devs will also add new features to this mode in the future.