An alpha value is a number 
such that 
is considered "significant," where 
is a P-value.
Alpha Value
See also
Confidence Interval, Hypothesis Testing, P-Value, SignificanceExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Alpha Value." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/AlphaValue.html