Obsidian Metadata can be added by adding a frontmatter section at the first line of the markdown document. Out of the box, Obsidian only supports the following metadata tags:

Key	Description
tag	Adds a tag to a note.
tags	Alias for tag.
alias	Adds an alias to a note.
aliases	Alias for alias.
cssclass	Allows for a custom style on individual notes using CSS snippets.

Source: help.obsidian.md