The Void is the seemingly infinite, mostly empty plane between dimensions. Unlike most other dimensions in The Multiverse, it is a unique existence, not affected by the creation of new timelines.
The Void exists outside any singular universe within the multiverse, and therefore doesn't necessarily follow their universal rules. A few examples of this include frequent gravitational anomalies, and time passing far slower. Unlike QRA or The Deep Void, however, the rules within it are simply lesser versions of the ones found in the rest of The Multiverse and aren't governed by pure chaos, due to its dimensional proximity to such an incredible amount of Gods.
Despite it's minimal energy, structures and creatures are not uncommon in certain areas. These are theorized to have been created through a mixture of background radiation from the different universes, universal energy from travelers passing through the dimension, and White Chara's presence.
The Void is essentially a lesser version of The Deep Void, and was historically the place where the barrier between the Bubble and The Deep Void was weakest. This has now been largely disputed with the emergence of QRA.
The Void is big enough to seemingly be split into sub-dimensions, if viewed by most beings. Every Chara in existence (including White) has their own "Void Room". These are in fact not their own, separate dimensions, but locations within the void. That said, the chance of any Chara finding the location of another's Void Room is practically impossible due to its sheer size.