Various Posts on Magento, SEO, Apple and Website design

Magento - Canonical Link Meta Tag / Data

Magento does not enable 'Canonical Links' as part of the default setup.

When enabled Canonical Links tell a search engine that a particular page is another version of an already indexed page. This is necessary because Magento will create many iterations of pages of the same product (and therefore product information) where that product exists in multiple categories. This can confuse / displease search engines - enabling canonical links will remove the duplication in the eyes of the search engine (the multiple pages will still exist online of course!)

The setting can be found in 

Admin | Configuration | Catalog | Catalog | Search Engine Optimizations: