As its sound might suggest, plaudit is indeed related to "applaud" and "applause." In fact it's really just a fancy way of saying "praise" or "acclamation."
Plaudit is used more in a literary sense than in spoken English, and particularly applies to the reception of a work of art, most notably a play. In fact, the word comes from the Latin plaudite, loudly uttered by Roman actors at the end of a play and meaning "applaud!" Kind of like cue cards for game show audiences now.
