What does designation VY, NML, UU in star names stand for?
VY Canis Majoris and UY Scuti are variable star designations. The first discovered variable star in a constellation is called R, the second, S, and then unto Z. After Z comes RR and so on. For a full description see this wikipedia page. NML Cygni is also a variable star, but its variable star designation is V1489 Cygni. The letters NML come from its discoverers: Neugebauer, Martz, and Leighton.