What is the difference between a vampire and a Noble in Noblesse?
Both terms were used by humans to describe the same species. The species refers to themselves as Nobles, and that's the name used for them throughout much of the series. "Vampire" was used for a relatively short time in the first issues, when the lore was yet being established.
The humans refer to Nobles as vampires because, as Frankenstein explains, Nobles can, and maybe did, consume human flesh and blood. In the series' universe the term "vampire" likely originated from Nobles, as well as the term "Noble" and "nobility" itself.
The term vampire was also used for the humans who were turned into zombie-like creatures by the humans who had obtained powers by making a contract with a Noble. One of those is seen early in the series, when he is turned by M-22.