1. Limp
2. Chubby - penis is waking up. Blood flowing. Getting longer and fatter. No stiffness.
3. Boner - penis is now upwards of 95% of its full size and is now hard. Is still limber and movable but stiff enuf to stroke properly.
4. Hard-on - 100% size. Very stiff now. Rigid comes into mind. A hard-on also is when you connect the inside and outside erection. Your cock is now at full attention. When u pull it down or to a side it springs right back.
5. Rager - highest level. This is achieved only thru a prolonged bate session with high end edging. A raging hard-on is a maxed out, fully pressurized, full blown, pulsing, beat red, explosive monster. An elite masturbator will recognize a chance to go for rage status and if accomplished correctly, can have his way with the level 5 beast in whatever way needed.