riding horse; saddle horse
Refers to a horse that is ridden, as opposed to a packhorse or draft horse. Common in contexts like horseback riding or historical settings.
He mounted his riding horse.
この牧場では乗り馬を貸し出している。
This ranch rents out saddle horses.
Compound of 乗り (nori, 'riding', from 乗る noru) + 馬 (uma, 'horse').