What is to boot?

"To boot" is an idiomatic expression in English that means "in addition" or "furthermore." It is often used to emphasize an additional point or to add extra information in a sentence. The expression is informal and can be used to highlight a positive or negative aspect that complements what has already been mentioned. For example, "She is a talented singer and an accomplished dancer to boot," suggests that being an accomplished dancer is an additional point in her favor.