Sass vs SCSS

SCSS is the newer and most used syntax.

It is more similar to normal css ("... every valid CSS3 stylesheet is valid SCSS as well.").

SASS:

$blue: #3bbfce
$margin: 16px

.content-navigation
  border-color: $blue
  color: darken($blue, 9%)

.border
  padding: $margin / 2
  margin: $margin / 2
  border-color: $blue  

SCSS:

$blue: #3bbfce;
$margin: 16px;

.content-navigation {
  border-color: $blue;
  color: darken($blue, 9%);
}

.border {
  padding: $margin / 2; 
  margin: $margin / 2; 
  border-color: $blue;
}

Credit: http://responsivedesign.is/articles/difference-between-sass-and-scss