They're charts of the bid and ask depth. Taking a single cross-section, and plotting it as a regular graph, you have something that looks like this:

(but with different colours)

On the x-axis is the price, the order-volume is on the y-axis. The bids are on the left, the asks on the right. A steep slope in for example the bid-section means that it'll take a lot of coins sold to decrease the price. Similarly on the ask-side, where a steep or vertical slope indicates a resistance to a price increase by buyers.

These types of graphs give an impression of the market sentiment beyond what the price tells you. A high volume on the bid side, means that the price is unlikely to decrease a lot for example.

The graphs that ChartBuddy posts are the same type of graph, but then many snapshots combined into a single chart, allowing you to see both the development of the price (where the red and green curves meet is where the price is at) over the last hour as well as the development of the depth. Whether there were any walls created or removed, etc...