cucsSwEthLanFlowMonRn is the Relative Name (RN) of a LAN traffic-monitoring (SPAN) session configured on a Cisco UCS fabric interconnect (a cucsSwEthLanFlowMon row) -- the naming fragment that distinguishes it from its sibling instances under the same parent object. UCS Manager builds the full DN by appending this RN to the parent's DN, so it is the piece an admin or script uses to tell this flow-monitoring session apart from others attached to the same parent. For instance, comparing the RN values under one parent quickly tells an admin which specific sibling -- among several instances of the same class -- this flow-monitoring session refers to.