A certain type of actor: camp, pompous, self-absorbed (but usually not a dick).
"Luvvie" is a slang word for actor originating in British theater, from the tendency of stage actors to call each other "love" and "darling." The people it refers to tend to be posh and classically trained, and it connotes a certain amount of pomposity, effusiveness, sensitivity, and/or sentimentality. As you might expect from that description, "luvvie" itself is a generally derogatory word, and this trope is double-edged: the existence of people like this in show business is obviously Truth in Television, and some actors will take huge offense at this perception of their profession, inevitably displaying all of the above qualities in the process of denying it. On the other hand, this trope is easy to overdo, especially in conjunction with an unfair portrayal of the whole art of acting as a self-indulgent sham requiring no work -- any actor who talks about their job in public at all, no matter with how clear a sense of proportion, stands a chance of being accused of being like this. Actors who possess a sense of humor often invoke or lampshade this trope about themselves for Self-Deprecation purposes. Expect to hear Continuity Lockout nicknames and references, long-winded stories about working with stars from the previous generation, Compliment Fishing, fits of rage and depression over bad reviews, catty remarks about some colleagues and gushing praise for others, obsession with who wins awards (while pretending not to care), and constant soul-searching and navel-gazing. A luvvie trying to function outside the context of work is often a sad sight to see. He may consider himself a a Sad Clown, Blessed with Suck for being so very talented in a world that doesn't understand. He may actually be that talented -- or not. Despite having any or all of these traits, these characters are often regarded affectionately -- this is usually Write What You Know, and after all, they have to be played by... actors. There are plenty of people in the real world who are massive luvvies and well liked for it. Compare Shakespearean Actors, Large Ham, Classically-Trained Extra, Wag the Director. A particularly unsympathetic portrayal might make them Nice Character, Mean Actor. They live in the same world as the Prima Donna Director and Caustic Critic. Luvvies are Always Camp, even the women.