What is a product key for any Microsoft software including Windows?

The serial is either on the back of a CD case for the software, or it will be in the documentation. Microsoft may also place it on a certificate of authenticity for Windows. You will know it is the key because it will be a mix of letters and/or numbers separated by dashes, usually about 25 characters long. You must have the key in order to install the software. You must install the software in order to use it. Therefore you can't install or use the software without this key. Installation will have a series of on screen instructions for you to follow. One of the boxes will request the key and have white boxes for you to type the key into. Type it in and click next or continue - whichever the button says - and the installation will continue.

The activation code is given to you when you first launch the software after installation. You will only have to enter this once. You have the option of using internet activation - which is the quickest and easiest - phone or mail activation. If you choose to do it by phone, choose the country you live in then it will give you a phone number to call. Call the number and give them your serial number and the activation number - both of which will be listed on the screen where you can easily see it. They will then give you the activation code that you will need to enter into the white boxes. Whichever you choose - Internet, phone, or mail - just follow the onscreen instructions to get the code. Contact Microsoft customer support to obtain a new key if you have misplaced yours. They will probably need some sort of verification, such as original receipt or bar code on the box or even the certificate of authenticity number. Of course, they will instruct you on how to obtain a new key and what is needed by you. Downloading the software without purchasing (retail versions) is illegal and it is called piracy. It is also illegal to use a key that you did not purchase because in this case you did not have to purchase the software either. Even if you have purchased the software and you use the Internet to find a key and use it - it is illegal - because if you really did purchase the software, Microsoft will help you obtain a new one. It is also illegal to use key generators (keygens), cracks, and no-CD cracks.

Note: This is a catch-all question. Neither it nor its alternatives should be deleted. It should also remain protected.
Every legitimate copy of the software has its own UNIQUE product key. If you have copied the software - you are committing piracy and the law-abiding members of the Wiki community will not help you.