Final answer:
A partial lunar eclipse occurs when the moon's orbit carries it through the penumbra but not the umbra, causing the moon's disk to just miss the umbral shadow.
Step-by-step explanation:
A lunar eclipse occurs when the moon passes through Earth's shadow. The shadow consists of two parts: the dark umbra and the lighter penumbra. If the moon's orbit carries it through the penumbra but not the umbra, it is called a Partial Lunar Eclipse. This means that the moon's disk just misses the umbral shadow.