What is "giddyup"

Usage examples of "giddyup".

And the upshot of his pondering is that Little Alfie scrapes up a few bobs here and there, and a few oats, and climbs on Governor Hicks one day and boots him in the slats and tells him to giddyup, and away he goes out of Miami, headed north, riding Governor Hicks and leading Last Hope behind him on a rope.

So maybe one deep pleasure is movement: giddyup, get along there, write one word, then another, turn that page.