The different sects or denominations of Judaism are generally referred to as movements. The differences between Jewish movements are not nearly as great as the differences between Christian denominations. The differences between Orthodoxy and Reform Judaism are not much greater than the differences between the liberal and fundamentalist wings of the Baptist denomination of Christianity.

In general, when I speak of "movements" in this site, I am referring to movements in the United States in the 20th century.

In addition, again from http://www.jewfaq.org/movement.htm   

Movements in the United States Today
Approximately 5 million of the world's 13 million Jews live in the United States. There are basically three major movements in the U.S. today: Reform, Conservative and Orthodox. Some people also include a fourth movement, the Reconstructionist movement, although that movement is substantially smaller than the other three. Orthodox and sometimes Conservative are described as "traditional" movements. Reform, Reconstructionist, and sometimes Conservative are described as "liberal" or "modern" movements.

Orthodoxy is actually made up of several different groups. It includes the modern Orthodox, who have largely integrated into modern society while maintaining observance of halakhah (Jewish Law), the Chasidim, who live separately and dress distinctively (commonly, but erroneously, referred to in the media as the "ultra-Orthodox"), and the Yeshivish Orthodox, who are neither Chasidic nor modern. The Orthodox movements are all very similar in belief, and the differences are difficult for anyone who is not Orthodox to understand. They all believe that G-d gave Moses the whole Torah at Mount Sinai. The "whole Torah" includes both the Written Torah (the first five books of the Bible) and the Oral Torah, an oral tradition interpreting and explaining the Written Torah. They believe that the Torah is true, that it has come down to us intact and unchanged. They believe that the Torah contains 613 mitzvot binding upon Jews but not upon non-Jews. This web site is written primarily from the modern Orthodox point of view. The 2000 National Jewish Population Survey (NJPS) performed by the Council of Jewish Federations found that 10% of American Jews identify themselves as Orthodox, including 22% of those who belong to a synagogue.

Reform Judaism does not believe that the Torah was written by G-d. The movement accepts the critical theory of Biblical authorship: that the Bible was written by separate sources and redacted together. Reform Jews do not believe in observance of commandments as such, but they retain much of the values and ethics of Judaism, along with some of the practices and the culture. The original, basic tenets of American Reform Judaism were set down in the Pittsburgh Platform. Many non-observant, nominal, and/or agnostic Jews identify themselves as Reform simply because Reform is the most liberal movement, but that is not really a fair reflection on the movement as a whole. The NJPS found that 35% of American Jews identify themselves as Reform, including 39% of those who belong to a synagogue. There are approximately 900 Reform synagogues in the United States and Canada.  For more information about Reform Judaism, see The Union of American Hebrew Congregations.

Conservative Judaism grew out of the tension between Orthodoxy and Reform. It was formally organized as the United Synagogue of Conservative Judaism in by Dr. Solomon Schechter in 1913, although its roots in the Jewish Theological Seminary of America stretch back into the 1880s. Conservative Judaism maintains that the truths found in Jewish scriptures and other Jewish writings come from G-d, but were transmitted by humans and contain a human compontent. Conservative Judaism generally accepts the binding nature of halakhah, but believes that the Law should change and adapt, absorbing aspects of the predominant culture while remaining true to Judaism's values. In my experience, there is a great deal of variation among Conservative synagogues. Some are indistinguishable from Reform, except that they use more Hebrew; others are practically Orthodox, except that men and women sit together. Most are very traditional in substance, if not always in form. This flexibility is deply rooted in Conservative Judaism, and can be found within their own Statement of Principles, Emet ve-Emunah. The NJPS found that 26% of American Jews identify themselves as Conservative, including 33% of those who belong to a synagogue. There are approximately 750 Conservative synagogues in the world today.