Wastelanders is a catch-all term for anyone living in the wasteland who is not affiliated with some other groups. They make a subsistence living off the land, trade with local settlements, and try not to be ravaged by the abundant, and usually hostile wildlife, or bands of roaming raider gangs. Most are not aggressive but will defend themselves if attacked. When that happens, they usually die, quickly.
Some wastelanders will not want to open dialog and tend to be rude, while others are pleasant and friendly towards the Lone Wanderer. They may be found as captives of super mutants or even as escaped slaves. Some can also be outright hostile, either before initiating conversation or immediately after ending conversation. Some of them may also sell you goods and repair items, these are known as scavengers and hunters.
Wastelanders can be found as corpses at various locations across the Mojave Wasteland. Because they are set as respawning non-player characters, they may sometimes be found alive, but with 0 health. They have no dialogue other than the constant "You mind your business, I'll mind my business" and some other lines of generic text.