What's to say? It's a holder for 8xAA batteries. Oh, and it has 8 channels. Did we mention it's black? And that it has a DC barrel plug. You might find that important...
These battery packs are common for powering Arduino boards and other development boards.
This battery box holder with a wire connector
Designed with a cap, and an on/off slide switch
Fit Battery: for 8x 1.5V AA Battery (Not Included)
Body Size: approx. 127 x 72 x 19mm/ 5.0" x 2.8" x 0.75" (L*W*H)
Cable Length: approx. 14.5cm/ 5.7"