CWR 
 Congestion Window Reduced (CWR) flag is set by the sending host to
indicate that it received a TCP segment with the ECE flag set (added to
header by RFC 3168).
ECE (ECN-Echo) 
 indicate that the TCP peer is ECN capable during 3-way
handshake (added to header by RFC 3168).
URG 
 indicates that the URGent pointer field is significant
ACK 
 indicates that the ACKnowledgment field is significant (Sometimes
abbreviated by tcpdump as ".")
PSH 
 Push function
RST 
 Reset the connection (Seen on rejected connections)
SYN 
 Synchronize sequence numbers (Seen on new connections)
FIN 
 No more data from sender (Seen after a connection is closed)



SEW: 
S is SYN, meaning it's starting a new connection.
E is ECE "indicate that the TCP peer is ECN capable during 3-way handshake"
W is CWR "Congestion Window Reduced (CWR) flag is set by the sending host to
indicate that it received a TCP segment with the ECE flag set"

tcpdump 'tcp[13] & 128 != 0' #CWR
tcpdump 'tcp[13] & 64  != 0' #ECE
tcpdump 'tcp[13] & 32  != 0' #URG
tcpdump 'tcp[13] & 16  != 0' #ACK
tcpdump 'tcp[13] & 8   != 0' #PSH
tcpdump 'tcp[13] & 4   != 0' #RST
tcpdump 'tcp[13] & 2   != 0' #SYN
tcpdump 'tcp[13] & 1   != 0' #FIN

ECN allows end-to-end notification of network congestion without dropping 
packets. ECN is an optional feature that may be used between two ECN-enabled 
endpoints when the underlying network infrastructure also supports it.