This is useful to look at when you are reviewing your typography settings in the theme and making adjustments.
Used for the Hero Headline. Typically, you only want to have 1 H1 on a page. This is per, Google's SEO and Local Search recommendation.
Section Headlines. Typically used for the main section headlines.
Typically used as a Section Sub Headings
Block Sub Headings and sometimes used for navigation links.
Alternates for nav and sub nav links
Body 1 - Section Copy
Body 2 - Block Copy
For typography details you can visit the Material UI documentation.