A path in the complex plane over which contour integration is performed to compute a contour
integral. When choosing a contour to evaluate an integral on the real
line, a contour is generally chosen based on the range of integration and the
position of poles in the complex
plane. For example, for an integral from 
to 
along the real axis, the contour at left could be chosen if the function 
had no poles on the real
line, and the middle contour could be chosen if it had a pole
at the origin. To perform an integral over the positive real axis from 0 to 
for a function with a pole
at 0, the contour at right could be chosen.
