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