if a match with a time limit (one-day international etc.) is stopped for any reason (poor weather for instance) while the chasing team are batting then play can't be resumed at another time, so the
Duckworth-Lewis method is used to determine whether the chasing team could have won the match in the remaining overs. It's a complicated calculation of run-rate, balls remaining and wickets that have already been taken, but the long and the short of it is a team with fewer runs can be awarded the victory with this method if they were maintaining a good run-rate before play is stopped.
this happened very recently! the series was tied 1-1 so the last one-day international was the decider. new zealand batted second and by the 35th over had 211 runs for 5 wickets, when rain stopped play. using the D/L method it was decided that they were over the required run-rate to beat the west indies' score of 293, so new zealand were awarded the victory and thus won the series 2-1.
by the time you have finished working this out the entire crowd has fallen asleep. this is why cricket is not a great spectator sport!