Kaldheim is both a plane (self contained world in the MTG universe) and the name of the first Magic expansion in 2021.
Kaldheim is a Nordic themed world. So you can expect Magic’s take on Norse mythology, vikings and other similar tropes.
We first heard about Kaldheim back in 2009. It was featured on a Plane card (from the Planechase set).
Theme Boosters make a return with Kaldheim. These are great as an intro-level product or for more casual players looking to grab a bunch of cards that match a particular color or theme. There are six different Theme Boosters available: one for each color, and a multicolor Viking booster containing cards that really hit that Norse Viking feel. Just like Set Boosters, Theme Boosters may contain some of the same 20 special cards only available in a few places. Each booster contains 33–34 commons/uncommons and 1–2 rares/mythic rares. Theme Boosters can also contain uncommon showcase cards!