I don't understand the "mb-sm-0" part in cards (bootstrap 5)?

Question

I did get what I expected but the thing is that I don't quite understand that part which says mb-sm-0

<div class="row">
  <div class="col-lg-4 mb-3 mb-sm-0">
    <div class="card">
      <div class="card-body">
        <h5 class="card-title">Special title treatment</h5>
        <p class="card-text">With supporting text below as a natural lead-in to additional content.</p>
        <a href="#" class="btn btn-primary">Go somewhere</a>
      </div>
    </div>
  </div>