What does Screening Efficiency mean? Screening Attenuation? Transfer Impedance ?

Screening efficiency means the ability of the outer conductor to prevent electromagnetic signals from outside to get into the inner conductor and to prevent signals from inside to radiate out through the outer conductor. There are many ways signals can penetrate into a connector/cable. Basically you can divide them into two types.

1. < 30 MHz Magnetic fields from outside induce electric currents in the outer conductor just like a magnetic field induces electric currents in a coil (transformer) or antenna.
This area is measured as Transfer impedance (ZT)

2. 30 MHz – GHz Both magnetic and electric fields are carried directly into the inner conductor through leaks in the outer conductor