What is refer PORT?

Table B-4 Version 5 Flow Record Format
Bytes Contents Description
0�3 srcaddr Source IP address
4�7 dstaddr Destination IP address
8�11 nexthop IP address of next hop router
12�13 input SNMP index of input interface
14�15 output SNMP index of output interface
16�19 dPkts Packets in the flow
20�23 dOctets Total number of Layer 3 bytes in the packets of the flow
24�27 First SysUptime at start of flow
28�31 Last SysUptime at the time the last packet of the flow was received
32�33 srcport TCP/UDP source port number or equivalent
34�35 dstport TCP/UDP destination port number or equivalent
36 pad1 Unused (zero) bytes
37 tcp_flags Cumulative OR of TCP flags
38 prot IP protocol type (for example, TCP = 6; UDP = 17)
39 tos IP type of service (ToS)
40�41 src_as Autonomous system number of the source, either origin or peer
42�43 dst_as Autonomous system number of the destination, either origin or peer
44 src_mask Source address prefix mask bits
45 dst_mask Destination address prefix mask bits
46�47 pad2 Unused (zero) bytes