I think he means the following, illustrated by example: instead of storing group_name in the users table for each user, you only reference a pk: group_id, and h

I think he means the following, illustrated by example: instead of storing group_name in the users table for each user, you only reference a pk: group_id, and have a separate table groups with the actual name. So the actual value "admin" will only be there once, defending against typos etc. So basically a normalised database