Alright kiddo, have you heard of the word "heresy"? It refers to beliefs or opinions that go against what is commonly accepted as true by a particular group or religion. In Judaism, heresy means having ideas or beliefs that don't match up with the basic teachings of the Jewish religion.
Now, let's get a little more specific. Judaism is based on the Hebrew Bible, which is also known as the Tanakh. It teaches that there is only one God, who created the world and has a special relationship with the Jewish people. It also teaches that there are certain laws and commandments that Jews should follow in order to live a good life and be close to God.
So, heresy in Judaism means having beliefs that go against these basic teachings. For example, someone might believe that there is more than one God, or that there are no gods at all. Or they might believe that the Jewish laws and commandments aren't important or don't need to be followed.
These kinds of beliefs can be seen as very serious in Judaism, because they go against the core values of the religion. People who are accused of heresy might face consequences like being kicked out of their community, or being shunned by other Jews. In some cases, heresy could even lead to more serious consequences like punishment by the authorities.
It's important to remember, though, that not everyone in Judaism agrees on what counts as heresy. Some people might have different ideas or interpretations of the core teachings, and that's okay! But when someone's ideas go too far outside of what's commonly accepted, they might be accused of heresy.