The MSCI World Index measures the market performance of 1,500 companies that have a global presence. It is often quoted by financial media to describe how the world's stock market is doing. However, it excludes stocks from emerging market countries, so it should really be considered a developed world index. The MSCI AC World Index includes emerging markets. "AC" stands for "All Country."
The MSCI Emerging Market Index tracks the performance of stock markets in 21 developing countries: Brazil, Chile, China, Colombia, Czech Republic, Egypt, Hungary, India, Indonesia, Korea, Malaysia, Mexico, Morocco, Peru, Philippines, Poland, Russia, South Africa, Taiwan, Thailand, and Turkey*. It compiles the market capitalization for all companies that are listed in these countries' stock markets. The Index is considered a good measurement of the stock performance of emerging markets.
The MSCI EAFE Index measures developed markets excluding the U.S. and Canada. EAFE stands for Europe, Australasia, and the Far East. The MSCI EAFE Index consists of the following 21 developed market country indices: Australia, Austria, Belgium, Denmark, Finland, France, Germany, Greece, Hong Kong, Ireland, Italy, Japan, the Netherlands, New Zealand, Norway, Portugal, Singapore, Spain, Sweden, Switzerland, and the United Kingdom.
MSCI also has indices for a variety of other geographic sub-areas, as well as global indices for stock categories such as small-cap, large-cap and the Gulf Cooperation Council (GCC) Countries. (Source: MSCI Index Definitions)