I mean that the term refers to regions that were formerly USSR/Warsaw Pact/communist for up to 50-80 years in the 20th century. What does Estonia have in common with Slovenia? What does Poland have in common with Georgia? The Baltics, Central Europe, Balkans, Caucuses, Black Sea, Karelia, Dnieper/Kiev region, Volga/Moscow region, and the Urals are all distinct regions with distinct history and culture that shouldn't be lumped together as "Eastern Europe"
Western Europe has commonalities like germanic/romance languages, feudalism, lasting French/German/British empires, and the origins of the EU, which can't be said for Eastern. It may even be more accurate to describe Western Europe as Scandinavian, West Germanic, French, Mediterranean, and British Islands. Either way, dividing Europe into an arbitrary East/West is just chauvinist neo-colonialism by Western Europe, where the countries of the EU project are treating the eastern frontier as a poorer, less developed "other". The EU project is meant to unite all Europeans as equals in democracy, and alienating former communist countries undermines that.
Video essay on the subject:
Western Europe does not have a monopoly on democracy and did not invent it, nor is Eastern Europe destined to restart 300 more years of Russian empire. Human rights and political progress does not care about geography.
Western countries like Spain and Germany were dictatorships for the majority of the 20th century and countries like Poland and Finland were democratic republics for large parts of the 20th century.
I think it's closed-minded to think of democracy as a western thing, and Russian imperialism as an Eastern thing, and it contributes to the political divide between the EU and its neighbors RU, BY, UA, MD, and GE.