Grid

A CSS grid is defined using the grid value of the display property; you can define columns and rows on your grid using the grid-template-rows and grid-template-columns properties.

The grid that you define using these properties is described as an explicit grid.

If you place content outside of this explicit grid, or if you are relying on auto-placement and the grid algorithm needs to create additional row or column tracks to hold grid cells, then extra tracks will be created in the implicit grid. The implicit grid is the grid created automatically due to content being added outside of the tracks defined.

In the example below I have created an explicit grid of three columns and two rows. The third row on the grid is an implicit grid row track, formed due to their being more than the six items which fill the explicit tracks.

* {
  box-sizing: border-box;
}

.wrapper {
  border: 2px solid #f76707;
  border-radius: 5px;
  background-color: #fff4e6;
}

.wrapper > div {
  border: 2px solid #ffa94d;
  border-radius: 5px;
  background-color: #ffd8a8;
  padding: 1em;
  color: #d9480f;
}

.wrapper {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr;
  grid-template-rows: 100px 100px;
}

<div class="wrapper">
  <div>One</div>
  <div>Two</div>
  <div>Three</div>
  <div>Four</div>
  <div>Five</div>
  <div>Six</div>
  <div>Seven</div>
  <div>Eight</div>
</div>