Why are some cables 'directional'?

Yes, the arrow points in the direction of the signal flow. While there may be some disagreement that the actual wire may be directional, there is general agreement that the shielding employed in these cables requires a directional connection.

The shield is terminated only at one end. This may or may not have any effect, depending on the noise environment of the system.

Twl:

I disagree with your arrow directionality (i.e. "points in the direction of signal flow"). Analysis Plus tells the user to point the arrows of their ICs toward the preamp/control amp. Probably like you say, has something to do with the shielding and grounding.

However, I do not believe that cables are directional re: signal only. As the current flowing through an audio cable is AC, by definition, it flows in both directions, not in one direction as in DC.

Sometimes, as in the shielded 300 ohm leadin from my FM antenna, the shield is left unterminated at both ends. What's best may depend on your particular equipment, and the environment it operates in. Try it both ways. One may be better, or there may be no difference. Or the whole one-end-terminated feature may be unnecessary.