A Developing country is a country that is living in mass poverty usually with low life expectancy low literacy rate low GDP and no access to medical care.
A Developed country is a country that has little poverty, although there will never not be poverty the economy is much more successful. There is a higher life expectancy there is a much higher literacy rate a high GDP access to reliable health care and clean drinking water.
Saudi Arabia is developing because there is around 10 to 20 doctors per 10000 people. Life expectancy is 65-70 years of age. The GDP is 100 to 1000 US Billion dollars. About 70 to 89 percent of males can read or write and 40 to 69 percent of Females can read or write.
Russia is developed because the life expectancy is 75 or more years, the literacy rate is 90 percent or more for males and 90 percent or more for females and the GDP is over 1000 billion USD and for every 10000 people there is 40 or more doctors.