Look at what Aleksandr Solzhenitsyn wrote in his book The Gulag Archipelago about the term “concentration camp”:
In August, 1918, several days before the attempt on his life by Fanya Kaplan, Vladimir Ilyich Lenin wrote in a telegram to Yevgeniya Bosh and to the Penza Provincial Executive Committee (they were unable to cope with a peasant revolt): “Lock up all the doubtful ones [not “guilty,” mind you, but doubtful–A.S.] in a concentration camp outside the city.” (And in addition “carry out merciless mass terror”– this was before the decree.)
Only on September 5, 1918, ten days after this telegram, was the Decree on the Red Terror published, which was signed by Petrovsky, Kursky, and Bonch-Bruyevich. In addition to the instructions on mass executions, it stated in particular: “Secure the Soviet Republic against its class enemies by isolating them in concentration camps.”
…The word itself had already been used during World War I, but in relation to POW’s and undesirable foreigners. But here in 1918 it was for the first time applied to the citizens of one’s own country.
The Gulag Archipelago, Volume 2, p 17