0 to arrange to have a seat on a plane, a room in a hotel, etc. -- ~を予約する
1 to not allow people to use something because it is only for a particular person or for a particular purpose -- ~を確保する, (使わずに)取っておく
This space is reserved for ambulances.
2 an amount of something that you keep until it is needed -- 蓄え, 予備
4 an area of land where animals and plants are protected -- 保護区
We can complete it step by step however long the road is and it can't be completed however short the road is if you don't even mark your footprint.
道路がどれだけ長くても、一歩一歩完了することができますし、足跡をマークしなければ、道路がどんなに短くても完了することはできません。