When I filtered HTTP traffic in Wireshark I bumped into a
X-FCCKV2 HTTP header in the collected info under the Hypertext Transfer Protocol.
I've researched it on Google but found nothing.
What does it stand for? Is it some kind of encryption?
X-headers can be added by the server or application for an applications own needs. What they mean is dependent on the app/server you analyzed, but which you didn't stated in your question.