grid-template-areas

/* Valeur avec un mot-clé */
grid-template-areas: none;

/* Valeurs de chaînes */
/* Type <string>      */
grid-template-areas: "a b";
grid-template-areas: "a b b"
                     "a c d";

/* Valeurs globales */
grid-template-areas: inherit;
grid-template-areas: initial;
grid-template-areas: unset;

<section id="page">
  <header>En-tête</header>
  <nav>Navigation</nav>
  <main>Zone principale</main>
  <footer>Pied de page</footer>
</section>

#page {
  display: grid;
  width: 100%;
  height: 250px;
  grid-template-areas: "head head"
                       "nav main"
                       "nav foot";
  grid-template-rows: 50px 1fr 30px;
  grid-template-columns: 150px 1fr;
}

#page > header {
  grid-area: head;
  background-color: #8ca0ff;
}

#page > nav {
  grid-area: nav;
  background-color: #ffa08c;
}

#page > main {
  grid-area: main;
  background-color: #ffff64;
}

#page > footer {
  grid-area: foot;
  background-color: #8cffa0;
}