A mule is the offspring of a male donkey (jack) and a female horse (mare). Horses and donkeys are different species, with different numbers of chromosomes. Of the two F1 hybrids (first generation hybrids) between these two species, a mule is easier to obtain than a hinny, which is the offspring of a female donkey (jenny) and a male horse (stallion).

Can we conclude that is a mule a cross between a donkey and a horse?
yes