The adjective boustrophedon means (especially of an ancient style of writing): having alternate lines written from left to right and from right to left.

This word is from the ancient-Greek adverb βουστροφηδόν, meaning literally as an ox turns (in ploughing), with allusion to the course of the plough in successive furrows.

In Originum sive Etymologiarum (The Origins or Etymologies), Isidore of Seville (circa 560-636), Spanish archbishop and Doctor of the Church, used neither βουστροφηδόν nor the Latin transliteration boustrŏphēdŏn but the Latin versus to describe this ancient style of writing:

Copyists and their tools (De librariis et eorum instrumentis) […] A verse (versus, also meaning “furrow”) is commonly so called because the ancients would write in the same way that land is plowed: they would first draw their stylus from left to right, and then ‘turn back’ (convertere) the verses on the line below, and then back again to the right—whence still today country people call furrows versus.
—from The Etymologies of Isidore of Seville – Stephen A. Barney, W. J. Lewis, J. A. Beach and Oliver Berghof – Cambridge University Press, 2006.

These are the earliest occurrences of boustrophedon that I have found, in chronological order:

1-: From The Leedes [sic] Intelligencer (Leeds, Yorkshire, England) of Tuesday 3^rd August 1762:

They write from Venice, that the Turkish Bashaw in the Isle of Candia, the antient Crete, lately caused some ground to be thrown up at the bottom of Mount Ida, when a tomb was discovered, in which was a leaden coffin, supposed to contain the ashes of one of the Grecian commanders at the siege of Troy. But in digging farther, they found a subterraneous cell, in which was a human skull, and a large roll of parchment, wrote in Phœnician characters, which appears to be the history of the Trojan war, compiled by Dictys of Crete, who is said to have lived before Homer, and was Secretary to King Idomeneus at the siege of Troy. This work is wrote in that antient manner called by the Greeks Boustrophedon, a word literally signifying furrowed writing. The Phœnicians wrote their lines alternately from right to left, and from left to right, in the same manner that ploughmen draw their furrows; from whence that kind of writing was called Boustrophedon.

2-: From the following advertisement, published in The Salisbury Journal (Salisbury, Wiltshire, England) of Monday 15^th July 1765:

B. Collins, Printer and Bookseller, on the New Canal, in Salisbury.
Where are sold the following prints, curiously engraved,
[…]
A curious print, eighteen inches long and eleven wide, (dedicated to the late Earl of Pembroke) of a very antient basso-relievo, among the antiquities of Wilton-House, the seat of the Right Hon. the Earl of Pembroke, brought from Smyrna, a city in Asia, which represents Mantheus, the son of Æthus, giving Thanks to Jupiter, &c. price 1s.
N. B. In the inscription on this relievo, which is a Grecian sculpture in white marble, of great antiquity, and much esteemed by the curious, are exhibited the form of the oldest Greek letters, and the most antient way of writing, viz. from the left to the right, and from right to left, called Boustrophedon.

3-: From Dr. Chandler’s Description of the City of Sigeum, published in The Gentleman’s Magazine, and Historical Chronicle (London, England) of October 1775—Sigeum was a Greek city in the Troas, an ancient region of north-western Asia Minor, of which ancient Troy was the chief city:

The temple at Sigeum was of remote antiquity, if not coeval with the city, which is said to have been built from the ruins of Troy. […] The celebrated inscription is on part of a pilaster, eight feet seven inches long, one foot and something more than six inches wide, and above ten inches thick […]. The lines in both inscriptions range from the left to the right, and from the right to the left, alternately. This mode of disposition was called Boustrophedon, the lines turning on the marble, as oxen do in ploughing. It was used before Periander; and by Solon, the Athenian lawgiver, his contemporary.

4-: From The History of Ireland from the Invasion of Henry the Second to the Present Times. Being a Compilation of the Philosophical and Statistical Points to be Found in the Most Approved Writers on the Subject. With Incidental Remarks and Moral Reflections (New York: Virtue and Yorston, [1778?]), by Sylvester O’Halloran (1728-1807):

The Greeks made use of another manner of writing which they borrowed from the Phœnicians, and called Βουςροφηδον; the meaning of which is, ploughing with oxen; as, like the ridges of a plough, it went in parallel lines from right to left, and from left to right. The Cionn fa Eite, or head of the ridge, and Cor fa Chasan, or reapers’ path, still met with in numbers of old Irish parchments, seems to have been formed on exactly the same plan, and wrote after the same manner; so that we may presume that the early Greeks borrowed this mode of writing also from our ancestors.

5-: From Lectures on Rhetoric and Belles Lettres (Dublin: Printed for Messrs. Whitestone, Colles, Burnet, [&c.], 1783), by the Church of Scotland minister and literary critic Hugh Blair (1718-1800):

The letters were, originally, written from the right hand towards the left; that is, in a contrary order to what we now practise. This manner of Writing obtained among the Assyrians, Phœnicians, Arabians, and Hebrews; and from some very old inscriptions, appears to have obtained also among the Greeks. Afterwards, the Greeks adopted a new method, writing their lines alternately from the right to the left, and from the left to the right, which was called Boustrophedon; or, writing after the manner in which oxen plow the ground. Of this, several specimens still remain; particularly, the inscription on the famous Sigæan monument; and down to the days of Solon, the legislator of Athens, this continued to be the common method of Writing. At length, the motion from the left hand to the right being found more natural and commodious, the practice of Writing, in this direction, prevailed throughout all the countries of Europe.