Business Objects are the basic building blocks and describe entities as persistency. An entity can be a customer, a product, a status, a telephone number and so on. To describe an entity, a modeling language needs to be able to describe name, description, attributes and the relations to the attributes, information about time- and text-dependencies, hierarchies and many more. Those entities are normally long living and need to be persisted.
Depending on the industry, business area or requirement for your business process, the same business object can look different. The entity material might serve as good example. While for a retailer the name of it might be "Article" and expiration date and nutrition facts are important, the very same object might be called "Product" for an oil company and needs attributes like sulfur-content and BTU.
A Business Process Expert needs to understand the requirement of the industry she is working in, in order to model business objects generically or to the right granularity.