This is the 4209th most frequent Japanese word.
予備
"予備" means "preparation" or "reserve."
予備 refers to a spare or backup item in this context.
私は予備の鍵を持っています。
I have a spare key.
予備 denotes preparation or additional supplies here.
登山に行く時は予備の食料を持参してください。
Please bring extra food when going hiking.
予備 represents prior or preliminary knowledge in this usage.