Here is a trick I use to define variables and keep them in some private scope, avoiding them leaking to the global space.

& {
  // Vars
  @height: 100px;
  @width: 20px;
  // Don't define any prop:value on this scope (as doing so will generate (wrong) output).
  .test {
    height: @height;
   width: @width;
  }
}
.rest {
  height: @height; // Name error: variable @height is undefined
}

Here, @height and @width are only defined for the scope created by & { ... }
You can also nest an scope inside a rule:

.some-module {
  @height: 200px;
  @width: 200px;
  text-align: left;
  line-height: @height; // 200px
  & {
    // Override original values
    @height: 100px;
    @width: auto;
    .some-module__element {
      height: @height; // 100px
      width: @width; // 200px
    }
    .some-module__element .text {
      line-height: (@height / 2); // 50px
    }
  }
  & {
    // Override original values
    @height: 50px;
    .some-module__another-element {
      height: @height; // 50px
      width: @width; // 200px
    }
    .some-module__another-element .text {
      line-height: (@height / 2); // 25px
    }
  }
}