A SYN scan looks like someone sending lots of SYN packets to different ports to see which ones are open. The target usually replies with SYN/ACK if the port is open or RST if it’s closed but the attacker never finishes the connection with an ACK An ACK flood is just a huge amount of ACK packets sent really fast, often from fake IPs, trying to overwhelm the target. There’s no real connection going on and the target might send RSTs or just get overloaded. Basically, a SYN scan is checking ports, and an ACK flood is spamming the server