Sass has two syntaxes.
The new main syntax (as of Sass 3) is known as "SCSS" (for "Sassy CSS"),
and is a superset of CSS3's syntax.
This means that every valid CSS3 stylesheet is valid SCSS as well.
SCSS files use the extension .scss.

The second, older syntax is known as
the indented syntax (or just "Sass").
It's inspired by Haml's terseness,
and is intended for people who prefer conciseness over similarity to CSS.
Instead of brackets and semicolons,
it uses the indentation of lines to specify blocks.
Files in the indented syntax use the extention .sass.