Difference between Godan and Ichidan verbs?

I'm aware of verbs classified as u verbs and ru verbs with the two exceptions. I've also read that all u verbs are godan verbs, and all ru verbs are Ichidan verbs. But I was unlucky trying to find a more profound explanation of what godan and ichidan are? Thanks for your help.

Those are just another names of -u verbs and -ru verbs, respectively.

godan verbs = -u verbs = consonant verbs = Group I
ichidan verbs = -ru verbs = vowel verbs = Group II

Japanese consonant and vowel verbs - Wikipedia, the free encyclopedia