For each section of your DNA, the Ancestry Composition feature assigns a probability to each reference population for a given segment of DNA. You can select the confidence at which these populations are assigned in the confidence dropdown.
The default Speculative Estimate corresponds to 51% confidence - this provides the most detailed view of your ancestry. You have the option to make the estimate more strict, meaning that the interpretation shown is more likely to be accurate. The Standard Estimate is at 75% confidence, and the Conservative Estimate is at 90% confidence.
You can read more about how the confidence threshold works in the "Aggregation & Reporting" section of the Ancestry Composition Guide.