"Maximum ratings are the extreme limits to which the chip can be exposed for a limited amount of time without permanently damaging it. Exposure to absolute maximum ratings for prolonged periods of time may affect the reliability of the device."
There are ESD diodes that can handle short transients/spikes if voltage exceed +-0.3V off VDD/GND, but they are not designed for continous current.
It's mostly the same thing up to the point at which it blows. The difference between zener (usually thought of as a clamp as it has a tighter knee making it more suitable for regulation) and esd/tvs is generally one of capacitance, which determines how fast acting it is.
