Laplace plane
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The Laplace plane is defined as the mean plane occupied by the orbit of a satellite during a precession cycle. In other words, the plane normal to the orbital precession pole of the satellite.
It is used to describe the orbits of satellites of gas giants. The "plane" is in fact a non-planar surface whose orientation in space is somewhat warped as distance from the planet increases. Roughly, for the satellites orbiting very close to the planet the Laplace plane is the planet's equatorial plane (being dominated by the planet's oblateness), while with increasing distance it warps or tilts until it approaches the orbital plane of the planet for its outer satellites (being dominated by the Sun). There are, however, some appreciable deviations from this rule. For example the Laplace planes for the satellites of Neptune are strongly influenced by the largest moon Triton, while for the outer satellites of Jupiter (Ananke, Pasiphaë and the others) the perturbations induced by Saturn are sufficiently important to make the Laplace plane deviate from orbital plane.
Note also that the Laplace plane will fluctuate in synchronization with the primary's orbital cycle because of the Sun's influence. When the planet's equator is edge-on to the Sun (planetary equinox), the latter won't distort the plane, unlike when the planet is pole-on to the Sun (planetary solstice).
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