What is martial law??

South Korean President Yoon Suk Yeol president declared marital law on Tuesday night so he could eradicate "shameless pro-North Korean anti-state forces". Protesters outside parliament shouted and clapped after Yoon backed down on Wednesday.
But what exactly is martial law and why are people so fearful of it? #SouthKorea #Korea #parliament #martiallaw #YoonSukYeol #military #7NEWS