Hi Bruno.
There have been many models of DI boxes (short for "Direct Inject").
The method started in the 1960's, and although Joe Meek, George Martin, etc, sometimes claim to be the first, it was actually Les Paul, in his home studio, who first dabbled in this.
Nowadays, you can also have a multiple output DI box, in order to record the direct signal, plus sending it to amplifiers too, thus recording the same performance through several flavors of sound devices.
Cheers