A “breadcrumb” (or “breadcrumb trail”) is a type of secondary navigation scheme that reveals the user’s location in a website. They are the links, usually above the H1 of the page or below the logo, that would look like:
Home > Category Page > Sub Category > Current Page
Breadcrumbs do have SEO and site user specific benefits, including:
User Experience: They allow your users to easily navigate your site by providing them with a visual keyword guide to what they may be seeking. They also encourage higher CTR from searchers when seen within search results.
Search Engines: They allow search engines to determine the structure of your site more easily and provide another mechanism to highlight important keywords for them to note in your navigation. They also provide added on-page SEO emphasis that highlights specific anchor text rich linking to internal pages.
Breadcrumbs should be tagged with Schema.org mark-up, across the website. More guidance here: https://developers.google.com/search/docs/data-types/breadcrumbs