The concept of the ``statistical significance'' of an observation, and 
how it is used in particle physics experiments is reviewed.  More properly 
known as a ``p-value,'' the statistical foundations for this concept are 
reviewed from a frequentistic perspective.  The discovery of the top quark 
at the Fermilab Tevatron Collider and a more recent analysis of data recorded
at Fermilab are used to illustrate practical applications of these
concepts.  

(To be published in the proceedings of the conference on 
``Advanced Statistical Techniques in Particle Physics,'' 
Durham, England, 18-22 March 2002.)