Refers to the act of riding a horse, often emphasizing the posture of sitting astride.
He is good at horseback riding.
sitting astride; straddling
Describes the posture of sitting with legs on either side of something, like a horse, a chair, or a person. Often used in compound expressions such as 馬乗りになる.
The child sat astride his father's back.
Compound of 馬 (uma, 'horse') and 乗り (nori, 'riding'), from the verb 乗る (noru, 'to ride'). The straddling sense is an extension of the horseback riding posture.