I recently noticed some plinths made out of four pieces of 15 or 18 mm MDF, about 300 x 900. Plus an end piece 300 x 300. So they formed a box 900 high and 300 x 300 in cross section.
I didn't take much notice until I had to move one and realised that they were not butted, not mitred, but had some routed edges. The shape meant that the corners meshed into each other and made very neat, straight lines.
Trouble is, I simply cannot think what router bits would do that. They surely must have some nice simple name?