@User: Grid-based routers work best when all pins of all standard cells are sitting directly on top of a route grid intersection, and a via can be placed cleanly on the point without having to be shifted to avoid causing a DRC error with some other nearby net. So "on-grid pins" mean all pins are nicely centered on grid intersections. I have not been spending a lot of time with the OSU cells for SkyWater, but the OSU cells I have worked with are all very nicely on-grid. The SkyWater libraries, by comparison, have a lot of pins off-grid and in very difficult-to-reach positions.