You may not be an astronomy buff, but still no excuse for going through life ignorant of its terms. An understanding of a Penumbral lunar eclipse is goal of this article. Timeanddate.com provides excellent explanation of Penumbral lunar eclipses below:
"Although the Moon is a dark object, it can be seen in the sky most of the time because its surface reflects the Sun's rays back to Earth. A penumbral lunar eclipse occurs when the Earth moves between the Sun and Moon but the three celestial bodies do not form a perfectly straight line. The Moon then travels through the outer part of the Earth's shadow (penumbra). This means...all of the Moon's visible surface still receives some...sunlight - but the Earth obscures parts of the Sun, as seen from the Moon."
A penumbral lunar eclipse is when the Moon travels through outer shadow cast by the Earth - called its penumbra! A handy eclipse calculator for your reference is available here.