breakpoint() is a Sass mixin that helps you compose media queries in an elegant way.

Here is a very basic example:

$breakpoints: (
    mobile:  320px,
    tablet:  740px,
    desktop: 980px,
    wide:    1300px
);

@import 'breakpoint';

.test {
    @include breakpoint($from: mobile, $until: tablet) {
        background: red;
    }
    @include breakpoint($from: tablet) {
        background: green;
    }
}

Compiles to:

@media (min-width: 20em) and (max-width: 46.24em) {
  .test {
    background: red;
  }
}
@media (min-width: 46.25em) {
  .test {
    background: green;
  }
}