Big bulge
Alex Weldon: This is a term coined in Charles Matthews' book Shape Up! and introduced to Sensei's on the Shape Problem 4 / Discussion page. I don't know much about it, except that it's a good shape, but I'm hoping that creating a page about it will serve as an inducing move to get those more knowledgeable than me to write about it. :)
Some people call this the boomerang shape.
Abstractly, the Big bulge is the shape formed by three stones with a keima-keima-ogeima relationship, as shown here. It's a good shape because it's flexible, but also very well connected.
I know of two common joseki that involve this shape. One arises from a 4-4 point one space low pincer invasion block, and looks like this.
The other joseki I know that involves this shape comes from the 4-5 point 4-3 approach keima joseki. It looks like this.
Charles If I can comment on the feeling behind the name: it came from examples like this one.
Here plays steadily for influence in the centre, to counter-act White's power there. (The game is Takagi Shoichi-Kobayashi Koichi (B) 1988-01-07.)
maruseru: This shape also occurs in Yu-Ch'ang-hyeok-Yi Se-tol (B) played 2000-12-20. This game (but not the particular move) is commented in Go-World #91 pp. 33-39.