Ay caramba, chica!
1/2 and 1/2 is the equivalent of single cream and light cream.
It was traditionally made by taking fresh, un-homegenzed milk, skimming the cream off of it, then recombining that cream with an equal amount of just-skimmed milk. In short, 1/2 and 1/2 is half cream and half milk.
As I understand it, the modern commercial process for making 1/2 and 1/2 is a little more sophisticated. But we can still make our own in the same time honored way of mixing cream and milk. Whatever. It's plus ca change or cuanto mas cambian las cosas -- no matter how you spell it.
Buena suerte,
BDL