The Scroll of Misty Step is a Common Scroll found in Baldur's Gate 3.
Scrolls are items that allow you a free cast of the Spell contained within. They can also be used by Wizards to learn the Spell in question. This consumes the Scroll.
The Scroll of Misty Step allows you a free cast of the 
Misty Step Spell.
Where to Get the Scroll of Misty Step in Baldur's Gate 3
The Scroll of Misty Step can be acquired through purchase from traders or by seizing them from a variety of containers and enemies.