HUGO takes markdown files along with TOML, JSON, or YAML and feeds that through the templates to create the site.
Front Matter in HUGO is the data that is included at the top of the markdown file along with some predefined variables that HUGO provides.
example:
---
someKey: "value"
someNum: 45
someBool: true
---
example:
+++
someKey = "value"
someNum = 45
someBool = true
+++
example:
{
someKey: "value",
someNum: 45,
someBool: true
}