The name for any number of staging points for attempts on Everest's (Sargamatha's) South Face, commonly near the terminus of the Western Cwm Glacier.
From Lonely Planet's Trekking in the Nepal Himalaya:
"Everest base camp is not actually a specific
site. Various expeditions have selected different
locations for a semipermanent camp during their
assault on the mountain... The trip to base camp,
while fascinating, is not as spectacular as the
ascent of Kala Pattar because there is no view of
Everest itself from base camp."