https://en.wikipedia.org/wiki/Subsatellite:
reply“A subsatellite, also known as a submoon, moonlet or informally a moonmoon, is a "moon of a moon" or a hypothetical natural satellite that orbits the moon of a planet”
It might be helpful to describe gravitational relationships with human generational terms of parent-child, grandparent-grandchild, sibling, cousin, etc. So the Sun is the Moon's gravitational grandparent and Jupyter is its parent-sibling (Aunt/Uncle, maybe pibling upwards and nibling downwards).
replyI had to look it up and it is theoretically possible, they could be called sub moons or moonmoon. I'm partial to the name moonmoon personally.
reply