(historical) The territory of the former Russian Empire inhabited by Ukrainians, approximately corresponding to modern central and eastern Ukraine.
(historical) The former Imperial Russian administrative subdivisions in north central Ukraine.
The term reflects the former status of Ukraine and Ukrainians in the Russian Empire, and went out of general use after the Russian Revolution of 1917. It is an anachronism, if not used in a historical context, and can be offensive to Ukrainians.
English Wiktionary. Available under CC-BY-SA license.