As the name suggests it is the management of reputation for any business or individual, It is the process of knowing what people are saying about you and to make sure that it matches your ideals. And it is done by influencing your target demographics through carefully designed posting and queries on social media.
Basically, it is a stealthier version of guerilla marketing to influence your existing and new customers by indirectly posting positive content and countering any negative content on any online platform.
This takes a lot of time and resources but still, many companies do it because it is a necessity in the digital age where one negative remark spreads like wildfire, your company will not shut down but it will hurt your reputation and it will show in your popularity and sales, so it is best to have established good relations with your online audience to keep the bad press at bay.