Broadly speaking, properties are either Freehold or Leasehold.
Freehold is where you own the property you're buying as well as the land it's on - like an ordinary house for example.
Leasehold is where you're buying part of the building, and you don't own the land it's on - like apartments.
Now, owning a leasehold property is usually fine. Everything should have been legally formed in a tidy and correct way, and there should be some management company that's taking care of the maintenance.
However, as with anything, when you start relying on these outside parties you have scope for issues to creep in. And with leasehold properties, they sometimes do.
What are Leasehold properties and should you buy one? How do they differ from Freehold properties? It's all covered here.