While viewing your store's pages, you will see a navigation path near the top left of the product listing. This path is known as the product's breadcrumb and it is intended to show your visitors their location on your website.
Typically, the store's breadcrumbs will use the "Home | [Page Name]" format. For example, if someone is viewing your store's blog, the breadcrumb will display as Home | Blog Home.
However, with products pages, the breadcrumb display is dependent on the product's assigned Category:
If the product is not assigned to a category, then the breadcrumb will display as simply the product's name
If the product is assigned to a category, the breadcrumb will display as Home | Parent Category | Product Name
If the product resides in multiple categories, the breadcrumb will typically display using the first parent category assigned to the product.