Final answer:
In a polyandrous mating system, one female mates with multiple males, as opposed to polygyny, where one male mates with multiple females. Polyandry is less common due to the typically greater investment females make in offspring care.
Step-by-step explanation:
A mating system in which at least some females mate with more than one male is termed polyandry. Based on Greek word origins, a polyandrous mating system is one where one female mates with many males. This is in contrast to polygyny, where one male mates with multiple females. Polyandrous mating is rarer than polygynous mating because it generally requires a greater investment in offspring from females, who usually provide the majority of care to their young.