A modern-day branch of the Jewish religion, Orthodox Judaism is the most traditional expression of modern Judaism when compared to Reform Judaism and Conservative Judaism. Orthodox Jews believe the entire Torah - that is, the "written law" (i.e. the five books of Moses) given by God at Sinai, which remains authoritative for modern life in its entirety. Orthodox Jews also hold to the "oral law" (i.e. the Talmud). According to a 1990 nationwide survey, 7 percent of American Jews are Orthodox. American and Canadian Orthodox Jews are organized under the Orthodox Union, which serves 1,000 synagogues in North America. Orthodox Jews reject the changes of Reform Judaism and hold fast to most traditional Jewish beliefs and practices. Orthodox Judaism has held fast to such practices as daily worship, dietary laws (kashruth), traditional prayers and ceremonies, regular and intensive study of the Torah, and separation of men and women in the synagogue. It also enjoins strict observance of the sabbath and religious festivals and does not permit instrumental music during communal services. Orthodox Jews consider Reform and Conservative Jews adherents of the Jewish faith, but do not accept many non-Orthodox Jewish marriages, divorces, or conversions on the grounds that they were not performed in accordance with Jewish law. The Orthodox Union dedicates significant resources to its OU Kosher division, which certifies an estimated 660,000 products in 77 countries around the world. The OU symbol is one of the most common certification symbols seen on kosher foods.