Wiktionary
n. (context US English) A drink consisting of milk and soda water with vanilla or chocolate syrup.
WordNet
n. made of milk and flavored syrup with soda water
Wikipedia
An egg cream is a beverage consisting of milk, carbonated water, and chocolate syrup. The drink contains neither eggs nor cream.
The egg cream is almost exclusively a fountain drink. Although there have been several attempts to bottle it, none has been wholly successful, as its fresh taste and characteristic head require mixing of the ingredients just before drinking.
Usage examples of "egg cream".
He sipped from an egg cream, which had neither egg nor cream in it.
Manhattan is a place of secret clubs, even a secret coffee shop on Lexington Avenue, a place where they serve perfectly ordinary coffee and danish and make a decent egg cream, all ordinary and nice, except it is a secret, and because it is a secret, is fought over by the endless stream of the newly famous who make the city at once so sad and so hilarious.
And I was shooting the breeze with her while I had an egg cream, and then I guess I went back to the building, and I wondered if Car—.
She celebrated by downing an egg cream from Rumpelmayer's ice cream parlor.