Canonical points to a different internal URL
This means that the URL in question has a canonical element pointing at another internal URL. The URL in question can therefore be described as 'canonicalized.'
Why is this important?
If Page A is canonicalized to Page B, it is explicitly marking Page B as it's canonical. This acts as a strong signal to search engines that these two pages should be considered duplicate, and that Page B should be prioritised.
It is important to note that a canonical is not a robots directive, so search engines may choose to ignore a designated canonical if they disagree with it. However, assuming that search engines honour the canonical, this means that Page A may become deindexed, and Page B will consolidate link signals (i.e. if Page A has some external links pointing at it, Page B will get the value for these links).
See Google's directions on defining canonicals to consolidate duplicate content.
What does the Hint check?
This Hint will trigger for any internal URL which contains a canonical link element (either in the HTML or in the HTTP header) which specifies another internal URL as the canonical URL. An internal URL is defined as being on the same subdomain.
Examples that trigger this Hint
Consider the URL: https://example.com/page-a
The Hint would trigger for this URL if it had either of the following;
Canonical link in the <head> to another internal URL:
OR HTTP Header canonical link to another internal URL:
Similarly, consider the URL: https://example.com/page-a?colour=red
The Hint would trigger for this URL if its canonical URL was the unparametrised version of the URL (or indeed any other internal URL);
Canonical link in the <head> to the unparametrised URL:
OR HTTP Header canonical link to the unparametrised URL:
Why is this Hint marked 'Advisory'?
In Sitebulb, this Hint is Advisory, as it does not represent a clear issue. Canonicals implemented in this manner are usually deliberate, so they are flagged in Sitebulb in order to draw your attention to the URLs that have been canonicalized, so you can double check that they have been implemented correctly.
While Sitebulb can check if a canonical tag is valid, it has no way of knowing for sure that Page B should be the canonical URL for Page A.