8-PSK:

Abbreviation for 8 bit Phase Shift Keying.

The animation below illustrates 8-PSK modulation in the I/Q-plane. Most importantly, 8-PSK allows for the simultaneous modulation of 3 bits into one symbol. Compared to GMSK, 8-PSK is therefore three times faster. However, the major disadvantage of 8-PSK modulation is that it includes amplitude modulation.
Note that EGPRS will not employ plain 8-PSK modulation but 3 PI/8 Offset 8-PSK-modulation. As illustrated in animation 2, this variant of 8-PSK limits amplitude modulation as there are no "Zero"-crossings.

 

Animation 1: 8-PSK Modulation in the I/Q-Plane

Animation 2: 3 PI/8 8-PSK Modulation in the I/Q-Plane