Basically, nothing. They are all exactly the same, have the same output qualities and do the same job. The main difference is simply the way that different amplifier manufacturers label their phono connections.

The only one to be careful of is Audio-Out which is slightly different to the others in the way that its output level is governed by the Volume control on the amplifier ( e.g. +10dB / -10dB ). Line-Out, Rec-Out and Tape-Out are "line level" only ( 0dB ) and are not affected by any alterations of the Volume control.