Meta data enhancement is a feature that can be used to add comments to specific frames when they are extracted to a new file. The main reason for this is to be able to mark frames that have been hit by a IDS signature, e.g. Snort (actually, the Snort alert.ids file is the only format that can be imported for meta data enhancement at this time):
Frame Indicator: the frame indicator column contains the criteria by which the frame is specified that should be enhanced with the comment. For TCP this should be the sequence number, for everything else it is the IP ID (this is not going to work for IPv6, since IPv6 does not have the IP identification value anymore except in fragmentation headers).
Prio: this is the priority value as specified by the Snort rule
Comment: when importing Snort alerts from a file, this column contains the SID and the rule name of the signature that was detected.