As the instance proceeds through the process, it is acted upon by various participants or processed automatically by software. For example, in a business process that handles purchases, each purchase order would be a process instance acted upon by such participants as shipping clerks, supervisors, and finance administrators.
Any number of instances can traverse a business process. For example, any number of purchase orders can traverse a business process that handles purchases.
Every instance has a specific history and properties. For example, a purchase order usually contains such data as a customer name, a list of items, an amount due, and dates of delivery and payment.
An instance can also have various status conditions. In the case of a purchase order, you want to know if it has been approved, billed, or paid, or if the requested products have been shipped.
Finally, each instance has a beginning and an end as defined in the business process.