This word is a chess rule, and the word "horse walking on the sun" is like walking on the Tian Zi, which is also an idiom.
Similar chess formulas are:
Horses are cavalry, so they are straightforward and oblique, so they go to the sun.
As a strategist, he guarded the camp, so he went to other places.
The car is a chariot, and it is on the rampage, so go straight.
A cannon is a cannon, and it is called a mountain, because it is fought far from a distance.
Scholar is a bodyguard, so he is on the edge of the general.
Of course, a piece like Jing Ke is gone forever.