Cafe con Leche literally translates to "coffee with milk." At McDonald's, it means espresso with steamed milk i.e. a latte. According to this NBC report, the "new" drink is essentially the same as a Latte, which basically means this is a re-brand to better appeal to the Hispanic/Latino market.
It must be noted that, at many establishments, a cafe con leche is virtually indistinguishable from a latte, so the re-brand actually makes quite a bit of sense. According to Wikipedia though, a cafe con leche is typically made with scalded milk (which has a different texture from steamed milk) and mixed in a 1-to-1 ratio. A latte, here in the U.S., seems more a 2- or even 3-to-1 ratio.
Cafe con Leche was also introduced as a drink option at McDonald's last year in South Florida
