The phrase refers to 1/8 of a Kilo of cocaine. Approximately 125g which breaks down to four full ounces in addition to 13g which is just short of a half ounce. The baby refers to the short half ounce.

Rapper Young Jeezy quotes a price of 'two grand flat' for this amount of the drug in his album Thug Motivation 101.
"Let me get an 1/8 of a bird."

"You mean four and a baby?"

"yes"

"Ok that will be two grand flat"
by Papa Calzone July 06, 2011
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One-Eighth of a Kilo of Cocaine = 125 grams
Not quite 4 1/2 ounces but almost.
Therefore, the extra 10-12 grams (Depending on how the Ounces are rounded) is refered to as a baby - more than a quarter but less than a half.
"Two grand flat get ya four n a baby"
Young Jeezy

($2,000 X 8 = $16,000 which is about the price of a kilo)
by Lucca Brassi March 26, 2009
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