Orbital Dynamicism is understanding how the orbits of a solar system work, and creatively disrupting them to your benefit.
Leveraging whatever capabilities you have is critical: it's quite common to slingshot an asteroid around three planets before it collides with the target, because setting it on that path is much more affordable than a direct orbital transfer.
Nearly every civilization does this, but with subluminal spacefarers it is often a matter of survival: they frequently have very little thrust capability and are desperate for resources.
Most superluminal civilizations groom their star systems, nudging planets into more forgiving orbits and insuring there are no unfortunate disasters waiting in the wings. It's never a fast affair, but it's something that the civilization benefits from every step of the way: endless tiny efforts eventually pay off.
Subluminal civilizations rarely have the time for these efforts to mature, either dying off or going superluminal long before orbital grooming becomes feasible.
However, the Transition Protectorate was a particularly adaptive, wide-spread subluminal civilization, able to become large solar sails on asteroids and moons. The remnants of the Zhad Database clearly show their organized, aggressive, and extremely patient efforts to analyze and exploit the orbits of literally every asteroid in every star system they inhabited.
There are many orbital disasters - no solar system is truly stable. While the timescales are immense, eventually something will go wrong. Even small disasters, like a subtle change in orbital inclination, can destroy a civilization.
The study of orbital dynamicism can help to determine upcoming disasters and counter them. But, as with any sufficiently powerful technique, it can also cause them.
Some say that the Cipher Volume is also caused by intelligent orbital grooming... but it's impossible to say whether it would be considered a disaster or a success without knowing more about the intent.