Indeed, concentration camps are for concentrating a lot of people in one place. It doesn't mean they are going to get killed.
This is the key element, and its emergence is one reason the Boer concentration camps are often cited as landmark developments in internment tactics. However, the Boer War example is neither the actual origin nor the sole line of descent for the "concentration camp" concept.
Up until the last half of the 19th century organized internment camps were basically only known from military POW internment / imprisonment facilities and certain restricted enclaves for compartmentalizing indigenous peoples (e.g., native American reservations).
The first official and organized use of internment camps for isolating (and in many cases passively disadvantaging to a fatal extent) a particular population arose in Cuba during the three wars of independence against the Spanish Empire (1868 to the late 1890s). It was in this context the label "concentration" was first applied.
This strategy of "concentrating" problematic populations via organized internment proliferated as soon as the Cuban wars ceased. The Americans had decried the Spanish camps in the run-up to the Spanish-American War, but adopted the concentration camp strategy in dealing with rebellious Filipinos during the Philippine War (1899 - 1902). This was the same period during which the British applied the strategy in the Second Boer War. A couple of years later the Germans employed concentration camps to isolate, control and passively decimate the Hereros of Namibia. And so on ...
These developments were facilitated by progress in communications, logistics, transportation, and management techniques that first made it possible to identify, locate and re-locate members of an arbitrarily-defined group.
The unspoken agenda of fostering deaths in such camps dates back to the Spanish in Cuba. Whether intended or not, the results from the earliest instantiations of the concentration camp strategy made it obvious such outcomes could occur.
The Soviet Union adopted this strategy (and accepted, if not sought, the potentially deadly results) in the gulag system from 1918 onward.
The Nazi innovation was to add the explicit intention to proactively exterminate and to industrialize the process by designing and operating camps for that purpose.
See, for example:
Concentration Camps Existed Long Before Auschwitz
https://www.smithsonianmag.com/history/concentration-camps-existed-long-before-Auschwitz-180967049/