One latte recipe, two URLs

Every byte on this page has a twin at a second URL here.

The same article at several addresses

Duplicate content is one piece of writing that a crawler can reach at several addresses. The usual suspects: the same article pasted onto two paths, which is this page's situation, a print version, a trailing-slash variant, or an http copy sitting beside the https original. One result twice helps no searcher, so the engine indexes a single URL and ignores the rest. The signals this page collected get divided between copies, and the copies now bid against each other.

Closing the duplicate

Choose the copy that should rank. Every other URL can then carry a rel=canonical tag naming it, or answer requests with a 301 redirect that lands visitors and crawlers alike on the kept page. Templated sites need watching: URL parameters and stray slashes mint identical pages nobody intended, and each of those pages leaks a little strength that belonged to your best URL.