Auto +X turns X misses into 1% hits. Activates at the last possible moment.
Fever +X reduces the number of 100% MAX necessary to fill the fever bar. I've heard it reduces the notes needed by X, i.e. +5 -> 45 notes necessary. After v. 1.23, it also makes the fever meter drain faster when you don't get 100% MAX; I don't know how fast that is, though.
Tech widens the timing window for notes.
Spec is the length of the health bar. It varies from gear to gear; the default one has 100.
Defup reduces the speed at which the fever meter drains when you hit notes inaccurately or miss them.