According to WebMD, MMR is the abbreviation for the measles, mumps and rubella vaccine. It is a two-shot series of vaccines to protect children from these illnesses. The first dose is given at 12 to 15 months and the second between 4 and 6 years of age.
Originally given as three separate vaccines, they were combined in 1971, states WebMD. As children enter school, parents must provide proof of vaccination. Rules by the Centers for Disease Control and Prevention state that adults born prior to 1957 may be exempt from the MMR shot, but this rule only applies to measles and mumps, not rubella.