keräilyaiheen
Keräilyaihe refers to a subject or theme around which a collection is built. It is the organizing principle that guides a collector's choices and determines the scope of their hobby. Essentially, it is what defines a collection.
For example, a person might collect stamps, and their keräilyaihe could be "stamps from the Soviet Union"
The choice of a keräilyaihe is often driven by personal interest, historical significance, aesthetic appeal, or