Being the shortest in length, time, distance, etc.; the shortest one.
この道が目的地までの最短ルートだ。
This road is the shortest route to the destination.
飛行機を使えば、最短で六時間で着きます。
If you take a plane, you can arrive in as little as six hours.
最短で済ませたいなら、事前に電話で確認しておいてください。
If you want to finish it as quickly as possible, please check by phone beforehand.