Short answers, pulled from the story.
Central Russia refers broadly to various areas in European Russia. Depending on the definition used, it can include all of European Russia except the North Caucasus and Kaliningrad, or it can refer to the more bounded ethnographical territory described by Stephen P. Dunn and Ethel Dunn as stretching from Novgorod Oblast in the north to the Ukrainian border in the south, and from Smolensk Oblast to the Volga.
The definition of Central Russia varies because it has historically been used for different purposes. It can function as an administrative designation, a geographic description, or a historical and ethnographical concept. The 1967 book by Stephen P. Dunn and Ethel Dunn, for example, treated it as the historical homeland of the Great Russians rather than a fixed political region.
In their 1967 book The Peasants of Central Russia, Stephen P. Dunn and Ethel Dunn defined the area as stretching from Novgorod Oblast in the north to the Ukrainian border in the south, and from Smolensk Oblast in the west to the Volga in the east. They treated this as a historical and ethnographical region, specifically the homeland of the Great Russians.
One common usage of Central Russia covers European Russia with the North Caucasus and Kaliningrad excluded. The North Caucasus carries a distinct ethnic and political character, while Kaliningrad is a Russian exclave physically separated from the rest of Russia by European Union territory. Both regions fall outside the cultural and historical core that the Central Russia concept typically describes.
According to a review of the Dunns' 1967 book, Central Russia as a historical and ethnographical concept refers to the territory historically associated with the Great Russians, the dominant Slavic ethnic and cultural group that shaped Russian civilization. This framing treats the region's identity as rooted in its people and cultural heritage rather than administrative boundaries.
The Peasants of Central Russia, published by Stephen P. Dunn and Ethel Dunn in 1967, focused on peasant life in the historical Russian interior. The authors used the historical and ethnographical definition of Central Russia, framing the region as the homeland of the Great Russians rather than a politically or administratively defined territory.