A device used by electricians to join wires together without soldering.

'Chocolate block' is a row of copper connectors, each of which has a screw in each end to hold a wire. The entire row is covered in plastic insulation, and can be cut to size. It gets its name from the resemblance to a bar of chocolate (or possibly a toblerone) the pattern of insulation over the screws forms.

A chocolate block looks like this:
from above:

     | <--- wire
 _   |   _   _
| |_| |o| |_| |  <---- Chocolate block
|o| |o| |o| |o|

from the side:

 ||  ||  ||  ||  ||  || 
The insulator has a series of 'chimneys' to allow the screws to be tightened with a thin screwdriver, but prevent the conductor being accidentally touched. Chocolate block can be screwed down to a surface, through a series of screw holes between the conductors. While more fiddly to use than twist-on connectors, chocolate block holds the wire more securely, and provides safer insulation. It also prevents wires from tangling together.

For a more unorthodox use of chocolate block, have a look at http://homepages.enterprise.net/jayjay/sheddy.htm