Product under test (PUT)

The Product Under Test, or PUT, refers to the complete, entire piece of software or the whole system that is being delivered for testing. Product is broader than "system" and might refer to the entire deliverable, including documentation, services, etc.' 

It is the finished article, the full package you are putting through its paces before it goes out to your users. Think of it as the whole house, ready for inspection. This term encompasses everything that makes up the final deliverable. 

It can get confused with the System Under Test (SUT), as those two terms can be, in rare circumstances, used interchangeably. Most often, they are mixed up by mistake. While the PUT is always the overarching software being worked on, the SUT is typically about the specific component, feature, or slice of that product that you are currently focusing your testing efforts on. Remember that the SUT is about the scope of what you are testing right now, which might only be one small part of the entire product. 

For instance, if you are building an online shopping website, the entire website is your PUT. When a tester is specifically testing the checkout process, that module or flow becomes the SUT for that particular session. Understanding this distinction, even if the terms get blurred in daily life, helps us be clear about the scope of our work and what we are doing.