Andy Pierce: Does this shape have a name?
This would be the table shape if was at a.
There are some circumstances where the table shape is too strong and too slow. This shape is a lighter, more flexible way to play. Black has the option of abandoning the stones if necessary when white tries (successfully) to cut through, usually getting a good result anyway. at b (the Trapezium Shape) is usually not good because a white play at a can then lead to the inefficiency of black having make an empty triangle with an additional play at c. at c is the bamboo joint.
Diagram as from Keshi and Uchikomi: Black makes a nice reduction. is bad here, overconcentrated with respect to the wall, accordingly, should be at a, followed by at either b or c.