This is just blocked packet, which is logged. (seems like your default behavior is block + log)
Some explanation
https://www.linuxquestions.org/questions/linux-newbie-8/how-to-read-iptables-logs-657599/
Window & RES are some inner stuff of IP packet, which takes a deep-dive. (tcp window?)
Mark is packet mark. This is locally assigned value, as used by loadbalancing, PBR and DPI. The value suggest me you're on load-balance config