Pony
Any horse or pony that leads the parade of the field from paddock to starting gate. Also, a horse or pony which accompanies a starter to the starting gate. Also can be used as a verb. He was ponied to the gate. Also known as a "lead pony."  

Post
1) Starting point for a race. 2) An abbreviated version of post position - He drew post four. 3) As a verb, to record a win - He's posted 10 wins in 14 starts.  

Post Parade
Horses going from paddock to starting gate past the stands.  

Post Position
Position of stall in starting gate from which a horse starts. 

Post Time
Designated time for a race to start.  

Preferred List
Horses with prior rights to starting, usually because they have previously been entered in races that have not filled with the minimum number of starters.  

Prep (race)
A workout (or race) used to prepare a horse for a future engagement.  

Prop
When a horse suddenly stops moving by digging its front feet into the ground.  

Pull Up
To stop or slow a horse during or after a race or workout.  

Purse
The total monetary amount distributed after a race to the owners of the entrants who have finished in the (usually) top four or five positions.