Ah, Urban Dictionary, where would the Internet be withoutcha?
1. A whipped iced dairy drink, usually chocolate, vanilla, or strawberry.
Wow, that milkshake from McDonald's was bangin.
2. A girl's body and the way she carries it.
Kelis' song 'Milkshake':
My whipped ice dairy drink brings the attention of many males to my place of residence and/or employment, and they declare that its quality far surpasses that of yours. Absolutely, it far surpasses yours. I could convey to you the recipe, but I would have to demand compensation.