What is wizards glass?

Wizard's Glass is a fantasy novel written by Stephen King. It is the fourth book in The Dark Tower series. The book is about the journey of a gunslinger named Roland Deschain, who is traveling through a mystical world called Mid-World to find the Dark Tower. The Wizard's Glass is a magical window that shows Roland his past, specifically his youth and the tragedy that led him on his quest for the Dark Tower. The book also introduces new characters, including Eddie and Susannah, who join Roland on his journey. Overall, Wizard's Glass is a pivotal book in The Dark Tower series and is widely regarded as one of Stephen King's best works.