The lowest speed reached during a corner. Minimum corner speed is one of the most important metrics in data analysis because it reveals how efficiently you are carrying speed through turns.
Going Faster! (Lopez) provides a data-driven example: "the slower driver loses more speed than necessary: he's 7 mph down at the turn-in, 2 mph down at the apex" compared to the faster driver. The text also reveals a counterintuitive insight about exit speed: "One determinant of corner exit speed can be the amount of tire scrub or drag against the road surface, which is created by large yaw angles. The steering wheel in the right-hand hairpin is turned 40 degrees left, indicating considerable yaw. The throttle was never modulated, yet the exit speed is lower than the car with less yaw." This demonstrates why minimum speed alone is misleading — a car with a lower minimum speed but less yaw at the apex can exit faster because less steering angle means less tire scrub and earlier full-throttle application.