Condenser tumble dryers differ from the usual vented ones in that they don't need to have a vent/hose going from the back of the machine to the outlet in your wall to take the steam out of your house.
This is handy because it means you can position the dryer anywhere you want.
The water from the drying process is collected in a tank which can be emptied when it fills up.There's quite a bit of info about this type of tumble dryer at
http://www.condensertumbledryers.org.uk/