The current Wikipedia page for evidence doesn't have any sources! Looking at the Scientific evidence page, things are a little better, but in the very first paragraph, we see the dreaded "citation needed".
Scientific evidence is evidence which serves to either support or counter a scientific theory or hypothesis. Such evidence is expected to be empirical and properly documented in accordance with scientific method such as is applicable to the particular field of inquiry. Standards for evidence may vary according to whether the field of inquiry is among the natural sciences or social sciences.Empirical, properly documented, applicable, all fine words, important words. Then we have standards, which vary.
This is of course, the very heart of the matter. Evidence. Evidence is the backbone, the foundation, the very essence of scientific knowledge.
Which means it is also the first thing to be attacked, doubted, criticized, dismissed, ignored or faked, when we deal with scientific issues which are under contention. Scientific issues which bring us into conflict. Into controversy, into matters of religion, faith, money, politics, greed, and any and all other human concerns, where the truth actually matters.
So what is evidence? Is the very definition up for a debate? Is there any governing body that decides? An authority we can seek for the answer?
Based on my research, there is not. There is no ultimate scientific judge who can slam a gavel down and declare, "This is evidence! This is truth! Accept it!".
In fact, fights over evidence in science are as bad as they are in the legal system.