The name Southerners used to describe Northerners who moved to the South during the Reconstruction era, between 1865 and 1877.
The term comes from the Carpetbags — luggage literally made from the pieces of old carpet — that were used by travelers during this period. Anyone with a Carpetbag was easily identified as an outsider. However, it was very much a derogatory term that suggested both political opportunism and exploitation by the outsiders. In the South, Northern carpetbaggers usually allied themselves with the newly-freed slaves to win political office.
It’s modern usage refers to any outsider who moves into an area to seek political power at the expense of the locals.