Metadata is simply data about your Elements.
Example: title, description, keywords, category, price. These are all your Elements' metadata.
You can input values for them one by one at the Edit Element page.
What is a metadata file?
For Artists with hundreds of Elements, it's faster and easier to input values in bulk.
For this purpose, you can use a metadata file.
A metadata file is simply a Google Sheets / Excel file that allows you the bulk input Elements' metadata.
To understand more, let's first export a metadata file of your Elements.