CSS Grid is a new layout system in CSS. It’s not a framework or library like Bootstrap – it’s built right in.
It allows you to take an element on the page and turn it into a “grid” of columns and rows. All of that item’s direct descendants will be “grid items” and placed within those columns and rows.
It’s not a replacement for Flexbox or floats, but an additional tool that works great in certain contexts. Here’s an article that goes into more detail about when to use Flexbox or Grid.