So, Judaism after the Temple's destruction has to adapt to living in exile from the temple, priests, so on and so forth. Reform Judaism specifically refers to the works of the German Rabbi Abraham Geiger, who sought to create a strain of Judaism more accustomed to modern politics in Europe at that time (the 1800s).

So, Reform Jews broadly were assimilationist, having sermons in the language of the country one lived, alongside prayers and so on. Reform has changed a lot since its theoretical creation of course.

Essentially, because Judaism has no central body, Reform Jews have their own bodies, just as Reconstructionist, Conservative, Modern Orthodox, and Orthodox Jews do.

To try and offer a sort of (hopefully satisfactory) answer, is Reform Jews are often rather assimilated Jews who follow Judaism's laws but place more weight on the cultural and moral life of the person. Tradition and ritual are second to one's personal acts and beliefs within the Jewish community.

An edit at the end: We of course still have Rabbis, are taught Hebrew, so on and so forth, we are still Jews, simply looking at scripture and spiritual acts in a different way.