A demigod is the offspring of a greek god and human. Also known as half-blood.
I thoroughly enjoyed every second of the episode. The episode basically goes through the first four chapters of the book. I really enjoyed that even though they are staying true to the book, they are makinig slight changes to help transition the series to TV. For example, the addition of the scene in the office where we see how Grover lies to get him kicked out of school. It shows the audience how dangerous Grover thought Percy staying at the school was and how he was protecting him from the sidelines without Percy knowing. In the books we learn that the school informs him that he would not be allowed to return, and he finishes the year. I feel to show that would of spent too much time at Yancy Academy when the story needed to progress.
They also added some elements that would only make sense if you read the books.