These are some personal shorthand names for different things that can go wrong with scenes...
Characters choosing the curtain materials
In any story, characters shouldn't be spending a disproportionate amount of time on their personal problems except insofar as those problems are important to the story as a whole. So their personal lives may have an impact on the greater story, but the personal life isn't the greater story. I was guilty of this to a large degree in the early versions of The One About the War. I didn't, at that time, have a firm grip on what was important to the story and what was important to the characters, which is not at all the same thing at all.
Confusion in this department leads to detailed scenes where the characters do lots of personal stuff which, while vitally interesting to them, is nowhere near as interesting to the reader. Moreover, it doesn't move the story forward. I call these "choosing the curtain material" scenes after realising that an early version of one of my novels had more or less a whole chapter where the couple set up their new home together.
I now try to avoid them when writing first draft and ruthlessly remove any that sneak in while I'm not looking.
Dwarves Drinking Soup
This term isn't one of mine; it was coined by fantasy author Juliet McKenna (jemck) after watching the DVD of Snow White and the Seven Dwarves. Apparently there was the usual Making Of extras and there was this scene that never made it beyond the pencil line-drawing stage of the animation. Snow White was ladling out the soup and the dwarves were singing a song called "Slurp Your Soup" and it was all lovely -- except that it did nothing to move the story forward or deepen characterisation. The scene wasn't saying anything that hadn't already been said, so it was cut from the finished version of the movie.
Ever since then, Juliet McKenna has used Dwarves Drinking Soup as a term that means more or less the same as Murder Your Darlings. However, Murder Your Darlings is often misused and misunderstood[*] and has very emotive overtones, so I prefer Dwarves Drinking Soup.
I came across it when she used it during a writers' workshop she ran at an Eastercon some years ago.
Day of the Ferrets
As coneycat points out over here, characters lecturing one another about stuff does not count as character development. Her post was prompted by a blatant example of plagiarism, namely the strange case a writer of romances inserting a post-coital discussion of ferrets into one of her novels. (Yes, ferrets! Said author has obviously never come across the British tendency to link ferrets with nether garments and the comic images that result from the intrusion of the one into the other.)
Now, as coneycat says,"there are times when they [ie lectures] feel natural--Patrick O'Brian used them sometimes, when the lubberly Maturin had to listen to Jack Aubrey talk about the sea. [...] However, there are circumstances under which infodumps, particularly one character lecturing another, will never work, and that's when the lecture seems to be happening for the mere sake of happening. There isn't any reason why we need to know this information, and the lecture seems to be prompted by nothing in particular. That's when I suspect the author is either showing off a new piece of information they've just learned... or just plain showing off, through the characters."
I feel this is a particularly tempting pitfall for the historical novelist who has done a lot of research and is damn well going to make sure it gets into the book. But it could likewise apply to fantasy writers who have researched something (looks sternly at self!).
[*] If you read the original advice to "murder your darlings", it was aimed at one particular writer and said about one particular piece of work. It wasn't intended as a blanket statement that you should automatically delete any piece of your writing that you are proud of, but I have seen it interpreted in that way.