Aspect ratio
Beginner
How tall a chip is compared with how wide it is. A ratio of 1 means a square.
Novice
Height divided by width (OpenROAD’s convention). A ratio of 1 is a square. Squarish shapes keep wires short in both directions.
Expert
Free to choose at the chip level, within limits set by the package and by how many pads or bumps must fit; for a block inside a chip it is negotiated with the top-level plan. A long, thin core lengthens wires along its long side and puts more wiring demand in one direction than the other.