Base Level
Every job class starts out at the Level 1. As soon as a character gains access to a job class, the character is Level 1 in that class, regardless of whether he uses the class or not. At this level, the character only knows the most basic abilities and can level up quickly by obtaining a small amount of job points.
In-Between Levels
The in-between levels for every job class are the Levels 2 through 7. During this time, the character learns the bulk of his abilities on his way to mastering the job class. Only characters that are assigned a specific job can level up that job.
Max Level
The maximum level for every job class is Level 8. Once the character obtains this level, he cannot level the job class any more. All job points obtained after reaching Level 8 go toward learning new abilities and do not affect the job class's level. Usually, once a character has a Level 8 job class, he will have learned most of the abilities for that job class.
Mastered
Characters can master any job class by learning all of the abilities associated with that job class. Theoretically, characters can master a job class without reaching Level 8, but the amount of job points required to learn every ability invariably results in the character obtaining a Level 8 job class before mastering the job.