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. However, it has a weakness when it comes to eyeshape. It looks like a rotated and stretched bulge. With one stone added, it becomes the throwing star shape.
Another joseki that involves this shape comes from the 4-5 point 4-3 approach keima joseki. It looks like this, with -- forming the shape.
Uberdude This shape does have a weakness, that I will forever remember as my teacher Willzhang, a chinese 6 dan, exploited it brilliantly. I forget the exact position, but I had some floating stones in the middle dominated by my opponent's thickness that were trying to make eyes. I played the big bulge shape, and he played at the shape point below which took away all my eyes. In the end I died. In the review he said I should have played the slower but more secure SakeBottleShape.