A donation TSD/TSS technique that got its name because of how the J covering the hole resembles a parapet. You can preserve the lines underneath, which often leads to situations where you can immediately follow up with a Tetris.
Compare with the alternative way to make the T-Spin shape assuming that you had the same initial field:
Compare Parapet with how you would build BT Cannon
Compare with placing a S or a Z which would have been possible if you didn't have a block on the position marked purple (see Cut Copy):
The Tetris doesn't always have to come after the TSD:
Here's an example where Parapet is a good option. You preserve the 4 lines underneath, so you can immediately follow up with a Tetris.
Here's an example of utilizing Parapet as a stacking alternative because the queue (OTLIZOS) did not have a J.
You can also forgo the TSD for a TSS. Useful when you don't have the initial height to make a Tetris because it preserves one more line in your stack. It also results in an equal row height on both sides, which arguably makes it a better option in many cases.
If you look closely, doing a TSS instead of a TSD results in an equal row height on both sides. This means that you can quickly build a TSD or another Parapet on top of the field afterward.
Below is an example of doing a TSS with Parapet. You preserve the 3 lines underneath, and because you're doing a TSS instead of a TSD, you keep one more line. This makes it easy to follow up with a Tetris.
Here are some other examples. The second one is an example of using Parapet while downstacking to subsequently clear 4 lines with a Tetris.
Sometimes you place the overhang first anticipating an L or J, only to realize that it's not in your queue. In that case, you can use a S or Z to skim. Like any other skim, this breaks B2B, and it would be best to avoid getting into this situation.