It can be said that the layout of a page is similar to the “floor plan” of the page. Page layout is the visual and structural composition of a page on your store. It is composed of many separate sections, or containers, which specify the area of header, footer, and content of the page. Through the layout setting, it can define the number of columns to each page. Magento 2 provides five extinct standard page layouts: one column, two columns with Left Bar, two columns with Right Bar, three columns, and Empty layout.
The content in a page is divided into different blocks, and then they are assigned to fill in the available space on each page. There might be some instances that the store owners want to reduce the number of columns in a page layout (let say from three to two columns). The question here is that whether the content is dismissed or retained and where it is stored. Magento 2 does support this function by expanding the content of the main area to fill in an appropriate space. For content blocks that are associated with the unused side bar, they seem to disappear from the page.
Another circumstance is when the store owner wants to increase the number of columns in a Magento 2 page. You might wonder that whenever you add a column to your Magento 2 page, do you have to rewrite the content that disappeared (in the first example). The answer is: “No, you don’t”. Thanks to the fluid approach, or liquid layout, in Magento 2 platform, the hidden content will reappear once you restore the page layout from 2-columns to 3-columns. Of course, you are not required to rework that content. This involves a different way of thinking compared to the individual HTML pages.