A DC motor uses Direct Current as apposed to AC (Alternating Current) which is what is produced from your mains power. Australia for example has 240V AC power.
A DC Ceiling fan will convert the AC power going into your fan from you home into DC.
DC Ceiling Fans have a number of advantages over their AC alternatives. The main one being they are far more energy efficient and also more reliable. Some DC fans can use up to 65% less power then a conventional AC fan. This represents huge savings on your electricity bill.
A DC motor is basically a fairly simple electric motor that uses electricity and a magnetic field to product torque, this in turn causes the motor to rotate, which in turn rotates the ceiling fans blades.