I've found a thread from a couple of years ago, on the same text - if this text was given to you by your school/university, why did they not include a proper glossary? So, a DM is a developed market. A developing market is a GM. This is the explanation given in the book, "Scarcity and Growth Reconsidered", edited by V. Kerry Smith.

It means "developed markets". These are countries where the economy and markets are efficient, open and transparent. Dow Jones and Standard and Poor's , for example, have each issued a list of what they consider to be "developed markets". The sentence is badly written. It may be more clearly written as: "This process is different in different countries. In developed markets, we expect steel production capacity to be reduced through company mergers. In China, it will be done by government orders."

developing (aka emerging) markets?