The radial engine is an internal combustion engine format most commonly used in early to mid twentieth century aircraft.
Unlike most engines that have the cylinders arranged in straight rows over a long crankshaft the radial has the cylinders set, well, radially on the same flat plane around a short crankshaft. This layout reduces the length of the engine, saving space and changing the center of gravity in ways that greatly benefited aircraft design.
The heart of a radial engine lies in the connecting rods. The rods all share a single bearing on the crankshaft as opposed to the one rod/one bearing set up of inline motors. The radial uses a rigid master rod with a flanged big end where all the other articulated rods connect. It is the master rod that rides the crankshaft and transfers power from the pistons to the shaft. This requires that the crank and rods be exceptionally heavy to take so much power in a compacted space. As the engine rotates around the master rod each cylinder is fired sequentially in the direction of rotation driving the crankshaft.

This format generates incredible power but the width of the motors and the complexity of the internal movements makes them impractical for any use other than in aircraft.

this node is pretty cursory, if anyone can do better, please do.