What is the difference between fermented milk (not sour milk beverage) and yogurt?

The newly released national food safety standard in 2010 stipulates that the products that can be called "sour milk" only use sour milk products fermented by Lactobacillus bulgaricus and Streptococcus thermophilus. The yoghurt products fermented by a variety of probiotics must be named "fermented milk". It can be simply understood that there must be more than two strains of fermented milk, and there are only two strains of fermented milk at most.