Obfuscated servers are special VPN servers that hide your data and the fact that you’re using a VPN connection. This technology is sometimes called as stealth VPN. Obfuscated servers are useful if you’re connecting from a place that heavily restricts internet usage, as they ensure that even your ISP (Internet Service Provider) won’t know you’re connected to an undetectable VPN.
Yes, it’s possible to see that you’re using a VPN by looking at your traffic patterns. That doesn’t mean your activities are visible, but your VPN use is. You can use obfuscated servers to hide the fact that you’re using a VPN.