MMR is a vaccine — one injection that protects a child against three illnesses at once: measles, mumps, and rubella (rubella is also called German measles). In many places, including Taiwan, babies have it at around thirteen months, and then a second dose at about four or five, so the protection lasts. Parents and nurses say “MMR” as if it were a name, not three words. You will hear it at the clinic and in talk about children’s health, not in casual chat about other things. It is medical English, but it is a very ordinary word for families.