Hi
Tagging/Untagging is not HP terms, its the Standards for 802.1q protocol (tagging protocol).
In Networking life, Tagging is allowing 802.1Q encapsulation to be carried over a link.
and Untagging is the normal operation mode of a single port by default.
Examples:
-If you have multiple Vlans and multiple switches, and you want to let Vlan traffic to pass all switches, then links between switches should be tagged for all vlans.
-A port connect to a PC should be untagged, because the PC will not understands the 802.1q (except in specail cases).
Check this:
http://www.hp.com/rnd/support/config_examples/5300xl_portbase.pdfGood Luck !!!