These are:
1. infinite consciousness,
2. infinite space,
3. nothingness,
4. no thought or non-thought;
They are helpful in combination with the 3 gates to Nirvana; i.e. Non-activity, Voidness, and Formlessness.
As the absorptions occur, one experiences bliss, by stillness — when one moves, they abate.
By remaining still, they occur more deeply; until non-duality and boundlessness.
All are passed before the moment of non-daulity, which is the first drop of enlightenment.
So — stillness as a gate to enlightenment is like this.