縦 means vertical, lengthwise and is a JLPT N1 kanji. It has 16 strokes and uses the thread radical (糸).
Stroke order · 16 strokes
On'yomi (音読み)
ジュウ
Kun'yomi (訓読み)
たて
Radical
糸 · thread
Strokes
16
How to remember 縦
Thread (糸) running up and down, following along (従) — vertical. 縦!! — 縦書き; Japanese books read right to left, top to bottom — the surprise of your first day!