Terror rule

[Toothpick]

Okay, dumb ass question time.

Can someone please explain to me how the terror rule works?
When a terror causing character/mount (tccm) joins a unit in combat, is the whole enemy unit terrorised, or just the stand that the tccm is actually touching?
If the tccm cannot make contact with an enemy stand, is the unit/stand still terrorised?
Or is the above all wrong?
(Pretty drawings would help)
Thank you.
Shane. 

[Aldhick]

Whole unit joined by tccm causes terror and any stand touching that unit (any stand of it) is affected by terror.

[Toothpick]

Thank you Aldhick.

[greenskinchief]

also the whole unit is immune to terror, regardless of which stand the character is with

[Toothpick]

Thank you Greenskinchief. Definitely worth remembering.