A stealth VPN hides the fact that you’re using a VPN. A regular VPN will already provide some obfuscation and privacy: your ISP (or anyone snooping around) will only see your encrypted online traffic and that you’re connecting to a VPN server. What websites you’re visiting would remain a mystery to them. But with a stealth VPN, the fact that you’re using a VPN will be hidden from prying eyes.
A stealth mode VPN is a VPN that hides the fact that you’re using a VPN. It is done by applying some clever encryption to the normal VPN data to make it look like normal internet traffic.