MDX Frontmatter is a way of adding information to the top of an MDX (Markdown + JSX) file. It's a powerful tool to provide metadata or other relevant information about the content that follows in the file. The information that is provided in MDX Frontmatter is typically in YAML format, which makes it easy to parse, serialize, and access. This allows us to define custom attributes and then access them in our MDX files. For example, we could use MDX Frontmatter to provide titles, descriptions, dates, authors, and more in our MDX files, allowing us to easily reference these values throughout our websites.