This would NOT have been suggested by Windows Defender.
Many fake reviews for this product (often companies with dodgy software like this set up "fake" websites to review their own product - and of course give it a glowing review).
NEVER install software that is suggested by an advert or pop up. My guess a piece of Malware (small program) was downloaded to your PC when you visited a website and this piece of Malware is what suggested you install it (perhaps pretending it came from Defender).
Download and install Malwarebytes and run that to rid yourself of any Malware.
https://www.malwarebytes.com/mwb-download/
If that does not get rid of Reimage then try to uninstall it. Or search the internet for hints on how to uninstall Reimage (however DONT install any programs that offer to uninstall it for you - they will probably be as bad a Reimage)