If you’ve read much Nabokov, you’ve undoubtedly run across the Russian word poshlost’—or “poshlust,” as that incorrigible punster Vladimir Vladimirovich liked to render it. He called it “smug philistinism” and wrote an entire essay, “Philistines and Philistinism,” about it (which you can read here): “Poshlism is not only the obviously trashy but mainly the falsely important, the falsely beautiful, the falsely clever, the falsely attractive. To apply the deadly label of poshlism to something is not only an aesthetic judgment but also a moral indictment. The genuine, the guileless, the good is never poshlust.” It’s a useful and appealing word, and it’s been picked up by others, some of whom are to be found in the Wikipedia article.
But it’s more complicated than that. Poshlost’ (пошлость) is the abstract noun from the adjective poshlyi (пошлый), which has a long and winding history, nicely summarized by Michele Berdy in this column:
The original sense was something that had “come into existence,” something customary, the way of doing things. In time it came to mean something “ancient” or “usual.” When Peter the Great was cutting short beards and kaftans, what was customary (пошлый) became negative. For a while it meant “low quality” (in other words, what’s old is no good). And then it came to mean something “devoid of meaning” or “trivial”: meaningless custom observed by habit.
(In Old Russian it was пошьлъ /poshĭlŭ/, derived from the verb ‘to go’ and virtually identical with the modern verb пошел /poshol/ ‘went.’) If you read Russian, there’s a good discussion of the history by V.V. Vinogradov here.
So the Nabokovian meaning is relatively recent, probably not much older than Nabokov himself. In the mid-nineteenth century it meant ‘common, banal, trivial,’ without the implication of philistinism that became attached to it later. When Baratynsky says, in his poem Осень (1836-37), “Глас, пошлый глас, вещатель общих дум” (‘Voice, poshlyi voice, prophesier of common thoughts’), he is using the older meaning, and so are Gogol, Pushkin, and other writers of the day. I fear that the prevalence of the Nabokovian meaning in the modern mind makes it easy to misread earlier writers.
Update. See this 2011 followup.