A business process or business method is a collection of related, structured activities or tasks that produce a specific service or product (serve a particular goal) for a particular customer or customers. (Wikipedia)
User interface and domain implementation are two key assets of an enterprise application. While the application consists of entities we do not build user interface which allows user to edit these entities and their relationships with each other directly. There is something else which dictates how we build the presentation for the user, the user tasks. Users care more about their problem than our how we have solved them. So though users understand the business domain and hence the entities but their objectives is to get the task fulfilled. A good user interface should allow for simple and fast realization of user's objectives. These tasks can be broken up into multiple user steps comprising a workflow. A workflow may involve multiple application transactions, each of which consist of one or more user step. In simple terms a user step really a fancy name for web page submits. A user should be authorized to perform a workflow completely or else we would call them different workflows. An application transaction is a unit of work which changes the state of the database. Producing something in the real-world may involve one or more workflows/tasks which we would call a business process.
Lets see what these concepts mean in the context of our sample application. The users of our application might define a client, create a loan, approve the loan and disburse the loan. Lets take a group of individuals who want a loan from the our bank. They care about the money paid to them and with information about repayment schedule. Defining a group involves finding a branch, creating a group, creating the clients in them and approving the group. Similarly creation of loan may have multiple steps involved in it. The fact that the their group has been created in our application isn't valuable to the group in the real world. In order to provide that value we would have to create, approve and disburse the loan. (In real-world identity verification of clients, providing cash to the group member would also be involved but that is not something which falls into the territory of our application). So lets map the concepts we saw above to our example.
Providing a new loan to existing group is different business process but uses some of the same workflows. In other words a business process is composed of workflows but it don't own them and other processes can also use them.