Duplicate Content
In one sentence
The same or nearly the same content reachable at more than one URL.
Analogy Mental model
Five identical copies of one book on the shelf. The librarian cannot tell which is the original, so recommends none of them.
In practice What you actually do
Point a canonical tag at the preferred version so the duplicates consolidate. Common sources worth checking: tracking parameters, HTTP versus HTTPS, www versus non-www, printable templates, and pagination that resolves to two different URL shapes.
Where people get burned Pitfalls
Duplication is not a penalty and it is expensive anyway, because signals split across versions and the engine has to guess which to rank. The guess is often not the one you wanted.
This entry was written in English from the Chinese original, not machine-translated. Read the Chinese version →