If you do not know, then ghosting is: “the practice of ending a personal relationship with someone by suddenly and without explanation withdrawing from all communication.” As with freelancing, as with life: it’s all about relationships. People are happy when you respect agreements and deliver within deadlines.
With the rise of remote work, communication is more and more important. In this context, ghosting is the biggest sin a freelancer can commit. Not only will you look pretty dull, but it will damage your reputation and you will be doing yourself a disservice.