What is aksauhini?

The word akṣauhiṇī refers to a military phalanx consisting of 21,870 chariots and elephants, 109,350 infantry soldiers and 65,610 horses. “One chariot, one elephant, five infantry soldiers and three horses are called a patti by those who are learned in the science. The wise also know that a senāmukha is three times what a patti is. Three senāmukhas are known as one gulma, three gulmas are called a gaṇa, and three gaṇas are called a vāhinī. Three vāhinīs have been referred to by the learned as a pṛtanā, three pṛtanās equal one camū, and three camūs equal one anīkinī. The wise refer to ten anīkinīs as one akṣauhiṇī. The chariots of an akṣauhiṇī have been calculated at 21,870 by those who know the science of such calculations, O best of the twice-born, and the number of elephants is the same. The number of infantry soldiers is 109,350, and the number of horses is 65,610. This is called an akṣauhiṇī.”

Source: A.C. Bhaktivedanta Swami Prabhupada (2014 edition), “Srimad Bhagavatam”, Ninth Canto, Chapter 15 – Text 30