Tetris Wiki

Parapet is a donation TSD/TSS technique which got its name because of how the J-Block covering the hole resembles a parapet. You can preserve the lines underneath with this technique, which often leads to situations where you can immediately follow up with a Tetris.

lllj
gggglgj
gggggggjj
ggggggggg
ggggggggg
ggggggggg
ggggggggg
lllj
gggglgpppj
gggggggpjj
ggggggggg
ggggggggg
ggggggggg
ggggggggg
lllj
ggggggggg
ggggggggg
ggggggggg
ggggggggg

You can also forgo the TSD for a TSS. It is useful when you do not have the initial height to make a Tetris because it preserves one more line in your stack.

gggglllj
gggglgj
gggggggjj
ggggggggg
ggggggggg
ggggggggg
gggglllpj
gggglgppj
gggggggpjj
ggggggggg
ggggggggg
ggggggggg
ggggllltj
gggglgttj
ggggggggg
ggggggggg
ggggggggg
ggggllltj
gggglgttij
ggggggggig
ggggggggig
ggggggggig
ggggllltj