Explanation/Reference:
Explanation
After you determine whether the prospective customer or an existing customer wants to purchase your product or service, you may close an opportunity. By closing an opportunity, you deactivate it, but you do not delete it. This gives you an option to reopen it later. When you close an opportunity, an opportunity close activity is created. It is represented by the opportunity close entity. You can use this entity to store information about the revenue, why you closed the opportunity, close date, and the competitor. It also contains the information about the user that created the opportunity.
References: https://msdn.microsoft.com/en-us/library/gg334362.aspx