"Sherpa" in upper case does properly refer to the members of a Tibetan ethnic group that is renowned for their mountaineering skills, However, when not used as a proper noun, i.e. lowercase "sherpa", it has come to have a variety of meanings from "local mountain guide or porter" to "the personal representative of a head of state or government who prepares an international summit". see
Sherpa (emissary) - Wikipedia
Sherpa and Sous-Sherpa are actual titles in the G7. for example see
Sherpa and Sous-Sherpa meetings
This is from project-himalaya.com
Sherpa ethnic group
With a capital "S", Sherpa is an ethnic group, one of the many pseudo-Tibetan ethnic groups that live at the higher altitudes in Nepal. The Khumbu, the Everest region from Namche and up to Everest Base Camp, is inhabited by Sherpas and there are pockets of Sherpas throughout the Nepal's district of Solukhumbu and close by.
And sherpa, the worker
Whereas "sherpa", uncapitalized, means a trek or expedition worker, a jack of all trekking trades who puts up and packs tents, serves meals (made by the cook) and walks/climbs with the the clients (also called members) during the day, ensuring they don't get lost and help them if tired or sick.
Of course, sherpa is derived from Sherpa, and all the first "sherpas" were from the Sherpa ethnic group, however, now there are trek and climbing sherpas from other ethnic groups too. Please take care with the distinction.
Personally, I feel that the BEST term for a sherpa who carries loads on Everest and other high Himalayan mountains is a "climbing sherpa".