Interesting - I was never sure of the terminology... Here are my own symptoms:
Shutdown: frozen in place, overwhelmed, can't do anything, can't think, can't talk, just stuck
Breakdown: crying, overwhelmed, helpless, hopeless, can't see any way out of my problems except to die
Meltdown: I never get violent or self harm
[EDIT:] Someone mentioned tantrums, and I remember reading once that the difference is that a tantrum is only done in front of other people, to achieve a specific purpose, and once the child gets what they want, the tantrum stops. Whereas a breakdown/meltdown is simply due to feeling overwhelmed, can happen when you're alone, and isn't an attempt to manipulate anyone else.