The very meaning of co-ownership indicates a division of property between several buyers of the same property.
Concretely, this means that you are the co-owner of the courtyards, balconies and stairs of which you have the common use with the other co-owners, and are owner of a part of the building, your apartment, of which you have the exclusive use.
There are two types of co-ownership: divided and undivided co-ownership.
A co-ownership is undivided if there is no material division of the property. The building is not shared, it belongs to several people at the same time. For example, spouses or siblings or friends who buy a duplex together are all joint owners, since only one property is registered with several names.
In an undivided co-ownership, the proportion of property rights between the co-owners is equal, unless the sales contract or an agreement between the co-owners provides for another division.
Inversely, in a divided co-ownership there is a material division of the propertyinto fractions. For example, a couple who acquires housing in a divided co-ownership, registered in the name of the buyer(s), will have the exclusive right on a private portion (apartment) and a share on the common parts (corridors, elevators, common service premises).
Divided co-ownership gives you the right to act alone on the private portion, which belongs to you. On the other hand, in undivided co-ownership, you cannot undertake a procedure alone because there is no division of the immovable property.