As I understand the way Carpe described it. Jobs would be Titles that have a Job Level but it doesn't level up doing normal combat but instead things like party play, companies, etc would earn you Job Points which would grant you access to skills specific to that Job.

Essentially your Job Title and your Weapon Class would be similar to the Job/Subjob system but both are equals at defining your character as a whole instead of one being only half your strength.

Job > Learn Job Specific Skills
Weapon > Learn Generic Skills that define how you perform your Job Specific Skills.

I think. He can elaborate better then I.