When you purchase an apartment in an immovable held in divided co-ownership, you become the owner of your dwelling (private portion), but also the owner of an undivided portion of the immovable designated as common portion (for example: the ground, balconies, major components such as foundations and main walls). This, taken as a whole, including the common and private portion, is designated in legalese as: a fraction.
The fractions may contain one or more private portions. They are described in the declaration of co-ownership in the Section entitled the Description of the fractions, and they are physically identifiable. They may include an apartment, but also a parking space or a parcel of land (for example in townhouses or semi-detached homes).