* Racking: This is a specific gait of the Tennessee Walking Horse, characterized by a four-beat lateral gait with a high, knee-action. It's not typically associated with "speed."
* Speed: This term generally refers to the speed at which a horse can travel, typically measured in miles per hour.
* Racing: This involves horses competing against each other at speed, often over a set distance.
It's possible someone is using "speed racking" as a colloquial term, but it's not a standard equestrian term.
Could you provide more context or clarification on what you mean by "speed racking"? Perhaps you were referring to something else entirely, or there might be a specific local or regional term that I'm not familiar with.