Acceleration
Also said as Ramp-up, Tight controls (when short)
The time a character takes to go from standing to top speed, and its partner deceleration, the time to stop again. Short feels tight. Long feels heavy or slippery.
These two numbers decide how much a player trusts their own landings. Long stopping time reads as ice, whether or not you meant it.
Say it
“Run acceleration should reach top speed in about four frames and stop in about four. I want it tight, not slippery, because the platforms are narrow.”
Where you’ve seen it
Celeste reaches full run speed almost at once, because its platforms demand precision. The characters in Super Mario Bros. take noticeably longer, which is why running there feels like building momentum.
Not to be confused with top speed
Top speed is how fast you end up. Acceleration is how long getting there takes, and it is the number people mean when they call controls tight.