<section>
  <div class="ballet"></div>
  <div class="cat"></div>
  <div class="gramophone"></div>
  <div class="sparrow"></div>
  <div class="sunset"></div>
  <div class="turkey"></div>
</section>

Without each:

section {
  div {
    width: 100px;
    height: 100px;
  }
  
  .ballet {
    background-image: url:("../img/ballet.jpg");
    background-size: cover;
  }
  .cat {
    background-image: url:("../img/cat.jpg");
    background-size: cover;
  }
}

Method 1:

$bg-pics: (ballet, cat, gramophone, sparrow, sunset, turkey);

@each $bg-divs in $bg-pics {
  .#{$bg-divs} { //first would be .ballet
    background-image: url("../img/#{$bg-divs}.jpg");
  }
}

Method 2:

@each $bg-divs in (ballet, cat, gramophone, sparrow, sunset, turkey) {
  .#{$bg-divs} { 
    background-image: url("../img/#{$bg-divs}.jpg");
  }