An echo is what happens when a statement, description, idea or story appears beyond its original source and begins to be repeated, expanded, supported, challenged or connected with other information.
Repetition is not the same as corroboration
One of the central ideas behind Why The Echo is that repeated information can look more independent than it really is. Ten pages can repeat one original claim. That is ten repetitions, but it may still be only one underlying source.
Why echoes matter
The wider picture is created by the combination of original voices, external sources, evidence, disagreement and context. Why The Echo follows those relationships to understand what the web actually appears to support.