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1.
noun: a plan or intention to attend 90 recovery meetings (almost always some form of 12 step meetings) in 90 consecutive days; usually follows form of verb 'to do'

"I'm going to do a 90 in 90 starting Sept 1."

noun: the process of attending 90 recovery meetings in 90 days: "I'm halfway through my '90-in-90'.
"I'm going to do a 90 in 90 starting Sept 1."

"I'm halfway through my '90-in-90'.

"Doing a 90-in-90 will really step up your program."
by racqg October 15, 2007