In database terminology, a schema is the organization of the tables, the fields in each table, and the relationships between fields and tables.
In FileMaker Pro Advanced, the structure is the organization of file elements such as scripts, layouts, value lists, and privileges. You interact with a file's schema through its structure.
It is also understood to include scripts, layouts, custom functions, menu sets, the security schema etc. Any of the things that we as developers create. In essence, anything but the actual data.