`@include` is used inSASS to apply the styles defined in a mixin to a selector. After defining a mixin with`@mixin`, you use `@include` to incorporate its styles. For example,if you have a mixin `@mixin box-shadow($shadow) { box-shadow: $shadow; }`, you can include it with`@include box-shadow(2px 2px 5px rgba(0,0,0,0.3));` to apply the shadow.