The Ba’ku live on the planet Ba’ku in Star Trek: Insurrection. The planet is located within a region of space whose metaphasic radiation produces powerful regenerative effects on living organisms.
The Ba’ku settled there after abandoning advanced technology and choosing a simple agrarian society. The radiation has preserved their health and slowed the visible effects of aging. Admiral Dougherty and the Son’a secretly plan to relocate the Ba’ku so the Federation can harvest the planet’s radiation for medical use.
Captain Picard and the Enterprise-E crew discover that the relocation violates the Prime Directive and the Ba’ku’s rights. Picard eventually opposes Starfleet’s plan and helps the Ba’ku remain on their world. The Ba’ku are the people, and Ba’ku is also the name used for their home planet. This differs from the Son’a, who are exiled descendants of the Ba’ku.