Under ProfitBooks, there are predefined names given for the ease of use.
For ex: Clients as Customers
Seller as vendors
However, the user can change such name as per there convenience through the settings page of ProfitBooks. One of such changes in this article is about changing name of Estimate to Sales quotation.
To change the name first you have to go to Settings page > Other Preferences like shown in the below picture:
Now you can change the default labels from drop down list. You can change the following labels: