A match point in the final of a tournament. Functionally the same as match point, but the term 'championship point' carries extra weight because there's a title on the line. At Grand Slams, championship point is the moment careers are defined. Serving out a championship point with an ace? Iconic. Double-faulting on championship point? That follows you forever.
"Championship point, Wimbledon final. He serves, the return comes back, and he puts away the volley. Champion."