This essentially means that you will have a lease over your flat as well as a share in the freehold of the whole building. This may be a share in a company that owns the freehold. Alternatively, the freehold may be held by up to 4 individuals. It is important to understand the responsibilities involved in having a share in the freehold which may include liability with others to repair and maintain the exterior of the building and the common parts.
More information you might find useful: