“The Fox Borrows the Tiger’s Prowess” is a classic Chinese 4-character saying.
狐 hú means fox, the modern word for fox is 狐狸
假 jiǎ in classical Chinese means borrow, in modern chinese this character means fake or a vacation.
虎 hǔ means tiger, in modern Chinese they add the character for old at the beginning 老虎
And 威 wēi is like the first character of the modern 威力 which means might or prowess
This chengyu, or 4-character saying, comes from a classical Chinese story.
One day there was a Tiger walking through the woods, looking for animals to eat, it came across a fox. The fox quickly thought of any excuse to convince the tiger not to eat him. He blurted out, don’t eat me, the heavenly emperor has made me the king of the animals! If you eat me today, you will be going against the will of heaven. The fox says if you don’t believe me, walk behind me, all the animals will run when they see me.
So the tiger really walked behind him and as the fox said, all the other animals ran. But the tiger didn’t realise that it wasn’t the fox they were running from, but the massive tiger behind him!
So this chengyu basically refers to when someone uses the reputation of someone or something stronger than themselves to intimidate others. It could be that small but provocative kid on the school playground, who is best friends with the school bully. He uses the bully as his backup to intimidate others.