BlackIce (also known as Black Frost or Black and White, not to be confused with Cold & Dark) is the name of the pairing between Jack Frost and Pitch Black from Rise of the Guardians. Much like Frostbite, BlackIce is not a popular ship in the Big Four fandom, but there are still many who support the relationship. Despite being a slash pairing, it is very popular in the RotG fandom.
Pitch Black shares one common thing with Jack that the Guardians do not; he knows what it is like to be alone and unbelieved in. It is one of the few sincere moments Pitch displays in the original film. They have a lot of interaction with each other, but their similarities don't stop here. Indeed, they both lost a loved one (Jack lost his sister while Pitch lost his daughter) that they both tried to save, and died for (Jack had saved his sister from ice, causing him to drown, while Pitch had been eaten by Fearlings by trying to rescue his daughter).
Fans either like to make the relationship a sincere friendship, a romantic relationship - two lonely people finding each other - or make it into a dependent, abusive one. Much like Hijack, BlackIce is commonly made for a more mature audience.