[oceanperch]

what exactly happens in seafloor displacment?

The media and here on FR the term keeps coming up but I don't understand it.

[Strategerist]

Displacement is simply a $5 fancy word for "movement."

The seafloor being displaced simply means it moved. In the case of a tsunami, either up or down, sometimes a considerable distance.

[capitan_refugio]

"strat" was basically correct. The seafloor changes location - it is displaced from where it was. The displacement can be compressional, tensional, or lateral (or a combination of lateral and another motion).

In this case, the seafloor on part of the fault-zone that moved, was raised as much as 10 meters. Think of what might happen if the bottom of a swimming pool was suddenly thrust up 10 inches - there would be a big wave of water spilling out over the edges. Now think of that on an oceanic scale with a few ten of thousands of square miles of ocean floor being thrust up as much a 35 feet.