A breadboard is a grid of sockets for developing electronic circuits and microcontroller projects, composed of conductive strips beneath the nonconductive cover. Because it is solderless, it's useful in prototyping, but more susceptible to falling apart when handled roughly.

The main grid, which is 10 columns wide and labelled a through j, has connections across every row, connecting a through e of every row, and f through j of every row. The 4 columns bracketing the main grid are all connected across every column, from the top of the board all the way to the bottom. These 4 columns are traditionally used as power and ground lines.

The medium breadboard is fairly versatile and probably the most commonly used size of breadboard in the physical computing lab. You can place multiple of them at various locations throughout the project and it won't get too clunky, yet a single one's still large enough to house pretty much all the connections you'd need on most projects.