Kan-on is based on the central Chang'an pronunciation. The name Kan could refer to the Han dynasty, which also had Chang'an as its capital city. Furthermore, Kan has also become a description for all things Chinese, e.g., Kanji ('Chinese characters').
Kan'on partly displaced the earlier go'on, which were "just imitations of Korean imitations, but Kan-on were imitations of the real things."
A minority of characters never had their Kan-on transmitted to Japan; their Kan-on are sometimes reconstructed in Japanese dictionaries although not specifically marked as such. A few dictionaries go as far as to discard attested Kan-on in favour of more systematic pronunciations.