REIT is an acronym for Real Estate Investment Trust, which is a company that owns either income-producing real estate (Equity REIT), or the mortgages of those properties (Mortgage REIT).
Shares of REITS are traded on major public exchanges, somewhat similar to stocks, which affords investors of different sizes the ability to invest in real estate through securities, while benefiting from the liquidity offered through the public exchanges.
There are different types of specialized REITS such as Retail REITS, Office REITS, etc. There are also different REITS focusing on a particular geographical region.
As long as REITs pay out at least 90% of their earnings in the form of dividends, the companies are not required to pay income taxes.