Secular Judaism refers to people who participate in some or all of Jewish culture without practicing the religion of Judaism in any form.
Secular Jews do not typically attend synagogue during Shabbat (Sabbath) nor keep the Torah in any meaningful way. Those who are secular Jews make almost no meaningful attempt to keep Kosher as part of this. Reform Judaism verges on secular Judaism.
Those who are born Jewish per Halakha (oral and written Torah) through the maternal lineage but who do not practice the faith are referred to as "Secular Jews," and may not practice even cultural aspects of Judaism. Such individuals include Albert Einstein, Bill Maher, Bernie Sanders, Judith Sheindlin, and all the members of the Three Stooges.
Perhaps, Jews are the group known for having the most enemies within. Because Judaism is more of a racial credo than a religion, it makes it harder to assimilate into other cultures. This is why typically in politics, Jews outside Israel lean left, but in Israel, they lean more right. Many Jews on the secular left don't care for Jewish interests, and some such as Leon Trotsky and George Soros admit this.