This page gives some terminology that is used elsewhere.

When buying stock we are buying a tiny bit of ownership of a company; when buying a bond we are making a loan to a company.  In either situation we would like to evaluate the greenness of the company.  Of course, it is impossible to reduce the activity of a company to a single number, or even a set of numbers, but it is useful to try.  Several financial firms such as MSCI (formerly Morgan Stanley Capital International) rate companies around the world according to many criteria.  One large category of criteria is Socially Responsible Investing (SRI).  A widely-used subcategory is ESG, a composite rating for Environmental, Social, and Governance performance.  ESG rankings typically entirely exclude major producers of alcohol, firearms, tobacco, gambling, pornography, genetically modified organisms, and nuclear power.  Notably, the ESG standard itself does not exclude owners, producers, or transporters of fossil fuels, but the so-called ESG mutual funds that I looked at all exclude such companies.  (For an extensive article on ESG, see Wikipedia.)

The ESG scores of companies can be used in various ways to select a group of companies for consideration, for example, those companies with the best ESG scores in various sectors.  The index for that group consists of the weighted sum of stock prices of the companies in the group.  This particular example could be called an ESG Leaders Index.  It is similar in concept to the S&P 500 index, except it uses a differently selected group of companies.  Other variations could restrict the inclusion to domestic or to foreign corporations, or to large capital companies, or in many other ways.  Acronyms abound, but the definition of any specific index can be found on the internet. An index stock fund contains stock shares or ETF (exchange traded fund) shares that try to approximate those in one of the published indexes.  An index bond fund is similar, but with bonds instead of stocks.  Many index funds are offered today.

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