There is confusing information regarding SYN flag.
The first paragraph says: "In information technology, a Christmas tree packet is a packet with every single option set for whatever protocol is in use.", and the second paragraph says: "When used as part of scanning a system, the TCP header of a Christmas tree packets has the flags SYN, FIN, URG and PSH set."
However third paragraph says: "Since Christmas tree scan packets do not have the SYN flag turned on, they can pass through these simple systems and reach the target host."
Christmas tree packets always have SYN flag set (please read RFC 1025 [Postel 1987]), else it's not a Christmas tree packet.
I was similarly confused and came here to make the exact same comment. It looks like SYN has been removed from the flags list, but the other problem remains; these two paragraphs are in complete contradiction. So what actually is a Christmas tree packet?