ecology block

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A large concrete block with a groove in the bottom face and a tongue on the top face to eliminate slippage when they are stacked. There is also a steel loop on the top face to facilitate lifting. The blocks are stacked in an offset manner to create a wall for retaining earth by means of their great mass. A wall built with them can be readily dismantled and the blocks reused (in ecological fashion).