'ghosting someone' is modern slang, mostly used with dating. Ghosting people means after the date, you just ignore them and don't reply to any of their messages, instead of saying that you're not really interested. It's basically one of the worst thing you can do and pretty rude. If someone ghosted you, your friends would tell you not to get involved with them again, cos the next time they contact you will be cos they are just bored. Hope that helps!