It's a made-up word. It has no meaning.
From Muggles' Guide to Harry Potter/Magic/Blibbering Humdinger at Wikibooks:
No description of the Blibbering Humdinger is ever given to us. From the fact that only Luna Lovegood seems to believe in its existence, we can safely assume that it springs from the fertile imagination of Xeno Lovegood, her father.
The Blibbering Humdinger is first mentioned in Harry Potter and the Order of the Phoenix when Luna Lovegood says that people used to think that they didn't exist. Hermione replies that they were right, because they didn't exist, causing Luna to slouch off, annoyed.
In Harry Potter and the Deathly Hallows, after the Battle of Hogwarts, Luna, seeing how tired Harry is, distracts the people around herself and Harry Great Hall by saying, "Ooh, look, a Blibbering Humdinger!" This allows Harry to don his Invisibility Cloak, and collect Ron and Hermione without anyone noticing.
Although it has no meaning, it might have been a play on words intended to convey the same kind of meaning as gibbering or blithering, which it sounds like a combination of. From both gibber and blither, respectively:
[Merriam-Webster]
: to speak rapidly, inarticulately, and often foolishly
: to talk foolishly or nonsensically : BLATHER
But that's purely speculation on my part.
Hermione's comment is mainly meant as a snide comment, referring back to her statement that no such creature exists. (But the syntax makes it sound as if blibbering is something that a humdinger does.)
Focal person doesn't have a special meaning apart from the literal words.
Google provides a good definition of focal:
relating to the center or main point of interest.
So focal person as it's used in your example would mean "person who is the center or main point of interest."
I get the feeling "leader" is what's truly meant/desired, but a neutral term has been used to prevent communicating that anyone has more power than anyone else. Business communication does this thing all the time across hierarchical boundaries (compare with the business-speak use of the word "partner", for example).
Best Answer
What was heard was Parseval, although it is often transcribed wrongly. Marc-Antoine Parseval des Chênes (1755 – 1836) was a French mathematician whose work preceded Fourier's (the class topic involves Fourier analysis).
Parseval's Theorem is often used to demonstrate mathematics software, including Maple:
Maplesoft
Reference is made to the scene in university mathematics courses:
The Good Will Hunting problem (Harvard Mathematics Math21b)