SILO comes from the word storage of grains in a deep hole for winter. It represents depth.

From SEO point of view, there are two types of structure, one is horizontal which we call flat structure and other one is vertical structure which we call SILO structure.

So, in flat structure all pages are linked to home page.

In Silo structure Under home page there may be number of categories of product or service

Under the product or services, there are more specific product or services, means every page will give you more detail about the same topic. And all these pages should be connected through internal links. The link should move from up to down and also down to up but the cross-category should not be linked.