The Oxford English Dictionary (OED) is a descriptive dictionary of the English language, published by the Oxford University Press. It traces the historical development of the English language, providing a comprehensive resource to scholars and academic researchers, as well as describing usage in its many variations throughout the world. The second edition came to 21,728 pages in 20 volumes, published in 1989. 

Work began on the dictionary in 1857, but it was not until 1884 that it began to be published in unbound fascicles as work continued on the project, under the name of "A New English Dictionary on Historical Principles; Founded Mainly on the Materials Collected by The Philological Society". In 1895, the title "The Oxford English Dictionary" ("OED") was first used unofficially on the covers of the series, and in 1928 the full dictionary was republished in ten bound volumes. In 1933, the title "The Oxford English Dictionary" fully replaced the former name in all occurrences in its reprinting as twelve volumes with a one-volume supplement. More supplements came over the years until 1989, when the second edition was published. Since 2000, a third edition of the dictionary has been underway, approximately a third of which is now complete.
when was the title first used unofficially?
In 1895, the title "The Oxford English Dictionary" ("OED") was first used unofficially