What does John 8:1 mean?

This verse begins the story of the adulterous woman, which seems to interrupt the flow of the prior passage. In fact, according to most scholars, this particular set of verses was probably not part of John's original work. Reading from John 7:52 directly to John 8:12 creates a single, uninterrupted flow of the story. Both the tone, content, and timing of this narration make it all but certain that this incident was not, in fact, meant to be included in this exact spot. However, based on other evidence, and its inclusion in various places in other manuscripts, the same scholars mentioned previously also agree that this is a true, legitimate story from the life of Jesus.

In other words, the tale of the adulterous woman is almost certainly not original to the gospel of John; however, it is a valid example of Jesus' life and teaching.