The connector (double-sided) that is on most shields, but without the actual shield board. To allow leaving a larger gap between boards (for heatsinking, or space for proto-board wiring on the double-sided connector protoboards.
...
----- <- other boards
-
- <- gap connector
-
----- <- proto board
-
----- <- processor board
...
Pretty much like the ribbon connector but without the actual ribbon in the way.
This could also be used to jam a lipo in the gap between boards and keep things nice and clean.