when the equivalence point of a titration is achieved..
Added:
(More precisely:)
The equivalence point is the point where the number of moles of
base equal the number of moles of acid. The end point is the point
where the indicator being used changes color (also 'indication
point)'.
If the indicator is chosen correctly, the end point will
essentially be exactly as near as possible at the equivalence
point.
The point of the titration is to find the equivalence point --
the end point is just a very close approximation to it. This is
because the pH of the solution changes very rapidly close to the
equivalence point.
Therefore, the indicator will change color very close to the
equivalence point because of the steepness of the pH change