The breadcrumb is a navigational structure that’s primarily at the top of the page, it’s a technique that is used to help both the users and search engines understand the relationship between each of the pages and the navigational sequence taken in order to land on that page.
Below is an example of a breadcrumb navigation on the Amazon website:
As you can see, the breadcrumb shows the sequence that was taken in order to land on that specific page. This demonstrates that the user navigated from the Literature & Fiction category, to Short Stories and then the United States. Each of these is linked to the subsequent page, therefore search engine crawlers are able to navigate between the pages in the sequence, this helps with indexing and transferring juice to the other pages in the sequence.
Here is another example of the breadcrumb structure used on the ASOS site:
In some cases, Google may also decide to include the websites breadcrumb structure in the search results: