Seems like it's just another way to say "perceived rise." Linked to spin rate. Here's what Sarris wrote in a piece about Walker Buehler:
There’s another advanced concept that’s at play here. “Ride,” or the way that a backspun fastball can counteract gravity and appear higher at the plate than a batter expects, is something that Buehler has used to guide his development.
Spin contributes to movement, and Buehler has the 12th-highest spin rate among starting pitchers in baseball this year. More spin on a four seamer generally means more ride. Buehler has more ride than the average pitcher, but only the 116th-highest ride since we started tracking these things in the early 2000s.
So why doesn’t he have more ride?
“Over 94, the ride matters less because it’s firm enough to not be perceived any different,” Buehler told me. “The guys that throw invisiballs throw 90-92, the ride helps them play so much further.”