Bosco is a chocolate syrup that you use to flavor milk or put on ice cream. I had never heard of it until it was used in an episode of Seinfeld called "The Secret Code." Bosco was George's favorite drink and he used it as the secret passcode for his ATM card. Much hilarity ensued.
George: Hi. I-I really should be getting back to my fiancé, you know, we, uh, we had this big fight yesterday and, uh, well she, she wants to-to know my secret code. I-I don't know, I can't tell her. The funny thing is, you know, I would really love to tell someone 'cause it's killing me. You uh, you wanna know what it is? It's Bosco. You know, the chocolate syrup? I love that stuff, I pour it in milk, it's my favorite drink. Hoo-hoo, boy, that is a relief!