Just in case a similarly befuddled audience turns to Google as its beacon of hope, I thought I'd document a few points of confusion I ran into, tonight:
In the Cisco world, where I've spent a considerable amount of time and training, a "trunk" applies to an interface on which VLAN tagging is applied. HP refers to this as simply a "tagged" interface.
Cisco refers to a set of bonded interfaces as a "channel-group", whereas HP refers to this same functionality as "trunking."
HP uses the term "untagged" and "tagged" to refer to Cisco's "mode access" and "mode trunk," respectively. This was my original point of confusion; i.e. what defined an "access" port and a "trunk" port on an HP switch...
Finally, in Cisco-land, an interface without a VLAN association has no configuration at all. To achieve the same thing, HP added a "no" mode at the interface level, as well as the usual disabled VLAN mode, globally.
Having worked with IOS for so long, fiddling with HP's SROS tonight was a bit of an impedance mismatch. The bottom line:
* Cisco "mode trunk" == HP "tagged"
* Cisco "mode access" == HP "untagged"
With that little bit of confusion resolved, go forth and bring HP and Cisco switches into heterogeneous harmony.