A Breadcrumb trail is a text based navigation showing users where in the hierarchy of the site they currently are, they also simultaneously provide a link to jump back up the hierarchy.
For example a breadcrumb trail for an entertainment site may read:
Home > Games > PlayStation 2 games > Sports > Pro Evolution Soccer 2008
This provides a significant benefit for SEO if the links in the breadcrumb trail are text links. For example the anchor text "PlayStation 2 games" in the example above provides search engines with relevance that this page sells PlayStation 2 games, this will lead to improved rankings for related search terms.
If optimised correctly these breadcrumb trail links are now not only user friendly, but each link acts like a vote for the page it is linking to.
Many people tend to use the word "home" in their breadcrumb trail when linking back to the home page. Although users will understand this link takes them back to the home page, it is beneficial to utilize a keyword rich word to aid the relevance to your home page. Other useful keywords you can utilize on your breadcrumb trial for ecommerce stores are "store" and "products".
When designing the site ensure you plan out the hierarchy carefully. Remember that pages higher up in the hierarchy will have more power. They will also be linked to more times in the breadcrumb trail, creating more votes for that page within the site.
It is also a good idea to make a breadcrumb link for your checkout process too. This tells shoppers where in the checkout process and how much longer they have to go. It will also allow shoppers to jump back to previous steps of the checkout process if they have made a mistake. This will lead to a better user experience and an increased retention of visitors.
In Conclusion, breadcrumbs trails are a great idea for usability and SEO and should be considered especially if you run an e-commerce store.
Paul
SEO Programmer