Maha means Great … But within the Vedic lore, since there can only be one great, the stated Maha (or Great) actually means Supreme.
Thus Mahapralaya (or Maha Pralaya) also known as Prakritika Pralaya means Great dissolution, which itself is the supreme dissolution.
This great destruction comes after the completion of the lifespan of Brahma (creator).
After Mahapralaya or Prakritika Pralaya starts, the entire multi-universe begins returning back to its original state i.e. macrocosmic voidness (which in other words also means voidness of allness or in other words, the stage of Sarva Shunya) and thence to the further state of Shunya Brahman (which in other words, means as the state of Zero Infinite which itself is realized to be the same as the Infinite Zero). As a matter of fact, Shunya Brahman is the real Shunyata of Buddhism …
After the multi-universe enters into this condition of Mahapralaya or Prakritika Pralaya, then the entire creation also rests for the same time span as was of the lifetime of that creator (Brahma) who had originated that multi-universe (which as such is dissolution during the stage of our currently discussed Mahapralaya) …
One single Brahma (or creator) has a life span of 311.040 trillion human solar years (as per middle time units of precession as were used by Vedic sages) … This time span is equal to “100 Brahma years (100 Brahma years means 100 years at the pristine abode of creator or Brahmaloka)” …
This is the stage when everything returns back to base nature (or root nature or Pradhan Prakriti or Moola Prakriti) which is also addressed as Maya Shakti (or divinity of illusion) of Brahma (or creator of allness).
And since Brahma has a total life span of 100 Brahma years (i.e. 100 Brahma Varsha) and as of now only the 51st year is running, so the time span of this great dissolution is still about 155 trillion human solar years away.