Top Definition
Combination of the words post and tsunami.

When something on a message board breaks and suddenly all the lurkers come out of the woodwork to complain.
"Holy shit, what are all these weird people doing on the forum posting all over the place?"

"It's a postnami. We're waiting for the admin to come on and fix the site so they'll go away."
by zexxxxxxxi June 28, 2012

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