A “breadcrumb” (or “breadcrumb trail”) is a type of secondary navigation scheme that reveals the user's location in a website or Web application. The term comes from the Hansel and Gretel fairy tale in which the two title children drop breadcrumbs to form a trail back to their home.

Breadcrumbs are used for navigation purpose. It is used to tell the user the path they have traveled in the website.

Breadcrumbs are an important part of the good website. They provide a good navigational path of the website. Google likes breadcrumbs as good way to figure out how the website is structured.Google Search uses breadcrumb markup in the body of a web page to categorize the information from the page in search results. Often, as illustrated in following use cases, users can arrive at a page from very different types of search queries.

Bread crumbs !!!
 

These are allow you to trace step from home page to currently viewing page,these are helpful to understand your website structure it will helpful to navigation of the website..

these links that allow a user to track their navigation on the website.
Like if you are on the mobile section page in the category in products section it will show something like this
Home->Products->Category->Mobile

A “breadcrumb” (or “breadcrumb trail”) is a type of secondary navigation scheme that reveals the user's location in a website or Web application. The term comes from the Hansel and Gretel fairy tale in which the two title children drop breadcrumbs to form a trail back to their home.