The core idea is that pension funds should only invest in companies which are socially responsible. In order to achieve this, pension funds/large investors assign (or outsource the assignment of) scores to each companies based on each company's "Environmental, Social, and Governance" practices. As these have become more and more standard, large corporations have started changing their policies to improve their ESG scores. Pushing companies to be more responsible for externalities sounds good and reasonable, but the implementation gives a lot of power to the people who define and calculate ESG scores, and like all metrics, ESG scores are flawed and gameable. (A common complaint is that companies can get away with dispicable behavior by gaming the scores in other categories.)
These scores are currently a big deal on the right, since they tend to be based on socially liberal values and tend to push companies into left-leaning policies, but the left should be just as concerned about the trend given that the trend is to reduce the diversity of policies among the very large companies which (seek to) control our lives.