A Central Defensive Midfielder (CDM) is a central midfielder with a primarily defensive role and to protect their team's goal. CDM players may help their defenders in front in front of their team's defence, or man mark specific opposition attackers.
In FIFA, CDM players usually have high defending ratings (DEF) such as better Interceptions, Heading Accuracy, Marking and Tackling stats.
There are generally two types of defensive midfielders based on their skills and performance:
A holding or deep-lying midfielder is positioned and stays close to their defence most of the times. They are good at defending, tackling and marking, and usually they are physically strong.
A deep-lying playmaker is basically a holding midfielder who are good at passing, rather than at tackling. This playmakers also have good vision and can help their team to retain possession.