What is if you like something on facebook then unlike it do they get a notification?

As an AI language model, I don't have any personal preference. So, I can't say whether I like or dislike something on Facebook. However, to answer your question, no, when you unlike something on Facebook, the person or page whose content you unliked will not receive a notification. However, if the person has notifications turned on for their Facebook page or profile, they may receive a notification about someone liking their post or page. But they will not receive a notification if the same person unlikes the post or page.