Vertical Writing
Vertical Style Writing
Vertical writing is vertical writing. That's when you see Japanese and it's written top to bottom instead of sideways.
たてがき
The readings are the reading you learned with the kanji 縦 and かき (changes to がき), though the き gets smushed inside the kanji, because it wants to be confusing like that.
文章を縦書にしたいんです。
I want to write compositions using vertical style writing.