Straight Up is a cocktail service term that has become a bit confused, as it can mean "up", in the sense of shaken with ice and then strained, or "straight", which means the same as neat, which is, poured directly at room temperature without ice.
Additionally, "Straight Bourbon whiskey" is a legal term which indicates a
bourbon whiskey
that is at least two years old, carry an age statement if any of the whiskey is younger than four years old, and not contain any added coloring of flavoring.