Character
A character is a fictional depiction of an entity, typically of a pony, human or supernatural/mythological creature that may or may not have a toy attached to their image.
Unlike many other toyetic franchises, including other Hasbro franchises, is that My Little Pony does not have a 'core' or 'canonical' group of characters it uses. Whereas Transformers will always feature Optimus Prime, Megatron, and usually Bumblebee, Grimlock and so on, comparatively few My Little Pony characters are recurring -- and the ones that are often share little more than a name and maybe a color scheme.
Fan characters made canon
A few fan characters have become canon, such as Roku-chan and Poniko, who were both mascots for a Japanese My Little Pony convention and appeared in the comics. Sappho and Marina are also examples of fan characters who became canon.