World seed
The in-game dialog for creating a new world. The seed input field can be seen below the name input field.
World seeds are displayed next to their names in world list in the main menu.
A world seed is a map seed used to initialize Valheim's pseudorandom number generator that determines how a world is generated. All worlds generated from the same seed will have the same layout for any given game version.
When creating a new world in the main menu, the game opens a dialog where the player can enter the world name and seed. The input field for entering the seed is initially filled with a random seed that can be replaced with a custom seed.